When the Met Office issues a Red Extreme Heat Warning, and temperatures reach 38°C, Britain’s caves, chalk streams, and ancient woodland hold temperatures that have not changed since the last ice age.
The surface of Britain is baking. The Met Office has issued a Red Extreme Heat Warning this week, with temperatures forecast to reach 38°C across parts of England. The shade under a garden tree barely drops the temperature by a degree.
But Britain contains cool places UK residents have rarely thought to visit, sites where the temperature has not moved in ten thousand years. Wookey Hole in Somerset maintains a temperature of 11°C every day of the year. The River Test runs at 10 to 12°C in July, fed by groundwater filtering through chalk for decades before it surfaces. Blue John Cavern in Derbyshire sits at 7-10°C, whether the surface above it is frozen in January or baking in June.
Britain built its cold into the geology. Most people have never been to any of it.
Region: England, Wales, and Scotland
Best for: Families, geology enthusiasts, walkers, history lovers
Getting there: Varies by location; confirmed transport details in each entry below
Time needed: Half a day minimum per site; overnight recommended for distant locations
Wookey Hole Caves, Somerset: 11°C Underground
The temperature drops the moment you step inside. Wookey Hole sits in the Mendip Hills limestone, where the River Axe resurfaces after running underground through a series of caverns carved over two million years. The cave system maintains a constant temperature of 11°C at every point in every season. On a day when Wells, three miles to the east, reaches 35°C, the air inside the entrance chamber feels like opening a cold room.
Archaeologists uncovered human bones, animal skulls, and Iron Age artefacts at the cave entrance. The Romans knew the site and left offerings at the water’s edge. What they noticed, as any visitor will today, is that the temperature inside never shifts regardless of what the surface is doing.
The cave tour runs roughly an hour and descends through a series of stalactite chambers. The underground river that carved the system is still flowing beneath you during the tour, audible in the lower sections when the guide group falls quiet.
Where to Stay: The Ancient Gatehouse Hotel, Wells. A 15th-century fortified gatehouse on the Cathedral Green, ten minutes from Wookey Hole.
Worth Knowing: Wookey Hole’s deepest accessible chamber reaches 84 metres below the surface. Divers have explored passages extending beyond two kilometres underground. The water temperature in the submerged passages stays within a degree of the cave air temperature above.
Chislehurst Caves, Kent: 35 Kilometres of Chalk at 10°C
Twenty-two kilometres southeast of central London, beneath an ordinary suburb in the London Borough of Bromley, there is a 35-kilometre network of chalk tunnels holding at exactly 10°C throughout the year. Workers cut the Chislehurst Caves over hundreds of years, beginning in the 13th century, extracting chalk and flint for building. The constant temperature comes from physics: the chalk mass absorbs and releases heat so slowly that the air inside equalises to the mean annual surface temperature of southern England.
During the Second World War, the caves sheltered 15,000 people per night. The tunnels contained a hospital, a church, and a cinema. The temperature that makes them useful during a heatwave also makes them survivable during the winter of 1940.
The guided tour takes about 45 minutes and departs regularly throughout the day. Bring a light layer: 10°C is welcome after 38°C on the surface, but it can feel cold against damp skin if you stand still.
Where to Stay: Innkeeper’s Lodge Bromley, Bromley. Four kilometres from the caves; straightforward, well-run rooms.
Worth Knowing: Jimi Hendrix performed in the caves in 1967, as did the Rolling Stones. The acoustics in the chalk passages attracted underground concerts throughout the 1960s.
Blue John Cavern, Castleton, Derbyshire: The Only Cave in the World With Blue John Stone
Castleton sits in the Hope Valley beneath Mam Tor and the Great Ridge. The limestone beneath the village contains more cave systems per square kilometre than almost anywhere else in Britain, and two are open to the public at the foot of Winnats Pass. Blue John Cavern runs into the hillside at 320 metres above sea level and maintains a temperature of between 7 and 10°C year-round.
The cavern takes its name from the rare purple-blue fluorite mineral found only on this hillside and nowhere else in the world. Veins of it run through the cave walls on the tour, exposed in the rock face above the lower chambers. The Romans mined it here, and pieces have turned up in Pompeii and in Roman sites across central Europe.
The cave tour takes about 45 minutes and passes through 16 caverns. Winnats Pass, the narrow limestone gorge at the cave entrance, funnels cool air down from the ridge. The walk from the car park noticeably lowers the temperature before you even reach the entrance.
Where to Stay: Ye Olde Nags Head, Castleton. A stone-built inn in the village centre with rooms and a reliable kitchen.
Worth Knowing: Blue John is only mined in winter. The cold conditions naturally stabilise the rock, reducing the risk of crack formation. The annual yield is tiny: around 500 kilograms extracted.
White Scar Cave, Ingleton, North Yorkshire: Britain’s Longest Show Cave at 8°C
White Scar Cave sits above Ingleton in the limestone country of the western Dales, at the foot of Ingleborough. Christopher Long, a student from Cambridge, discovered it in 1923 by following the sound of water into a previously unknown entrance on the hillside. Today, it is Britain’s longest publicly accessible show cave, running 1.5 kilometres into the limestone at a constant temperature of around 8°C.
The tour passes formations built over 120,000 years. The flowstone floor of the main gallery reflects the ceiling in standing water, and the lower sections sit directly above an underground stream audible through the rock below. The cave temperature barely registers a seasonal change. The 8°C you encounter in June is almost identical to what visitors experience in December.
The same Ingleborough limestone that shelters this cave also feeds the nearby waterfalls above ground. Our guide to the waterfall walks in Wharfedale covers the wider limestone country, which is worth combining with a cave visit. Ingleton sits 30 minutes from Settle on the Ribble Valley rail line.
Where to Stay: Springfield Guest House, Ingleton. A well-reviewed guesthouse a short walk from the cave entrance, with views up to Ingleborough.
Worth Knowing: White Scar is the only commercially open cave in Yorkshire. The main waterfall chamber, reached in the second half of the tour, marks where the underground stream from Ingleborough meets the cave at surface level. Visitors can hear the water level change between tours as rainwater moves through the system above.
The River Test, Hampshire: Chalk Streams That Never Exceed 12°C
The River Test rises in the chalk hills above Basingstoke and flows 64 kilometres southwest to Southampton Water. Unlike most English rivers, which warm throughout summer as surface water heats in sunlight, the Test is fed almost entirely by groundwater that filters slowly through the chalk aquifer beneath central Hampshire. This water surfaces at 10 to 12°C regardless of the season. It takes the full length of the river before the stream warms noticeably.
Fewer than 230 chalk streams exist in the world. Over 85 per cent of them are in England. The Test is one of the finest. The water runs clear enough to count gravel at a depth of three metres. Wading in below Stockbridge on a hot afternoon drops body temperature within seconds.
Public access is limited in places, as fishing estates own much of the bank. The National Trust maintains access along sections near Mottisfont, where the grounds of Mottisfont Abbey run down to the river’s edge.
Where to Stay: The Greyhound on the Test, Stockbridge. A riverside inn on the main street, three kilometres from the Mottisfont access point.
Worth Knowing: The River Test gave Britain fly fishing. Victorian anglers on the Test and Itchen developed the technique of casting a dry fly on the surface during the late 19th century because the chalk water transparency made conventional bait fishing ineffective. The fish could see the hook.
Wistman’s Wood, Dartmoor, Devon: Ancient Oaks on the Open Moor
Most of Dartmoor offers no shade. The open plateau carries no tree cover for miles in any direction, and on a clear day in a heatwave, the granite reflects rather than absorbs heat. Wistman’s Wood is the exception. Sitting at 380 metres above sea level in the West Dart Valley, this ancient oak woodland covers roughly two hectares of granite boulders on the open hillside.
The oaks are among the oldest in Britain, likely at least 500 years old, though some estimates put them considerably older. They are gnarled, horizontal trees barely two metres tall, growing directly out of the boulders and covered entirely in moss and lichen. The canopy is dense enough to noticeably lower the temperature inside, and the humidity within the wood makes the air feel different from the baked moorland beyond its edge.
A four-kilometre walk along the West Dart from the Two Bridges car park leads through the valley to the wood. The path is unmarked for much of its length; the AllTrails app carries the route file.
Where to Stay: Two Bridges Hotel, Two Bridges, Dartmoor. The hotel sits at the foot of the walk, directly beside the West Dart River, with Dartmoor on three sides.
Worth Knowing: Research by the University of Exeter confirmed Wistman’s Wood as a remnant of post-glacial forest cover, not a later replanting. The naturalist Richard Polwhele described it in 1797 as one of the most ancient woodland survivals in southern England. It was old when he wrote that.
Dan yr Ogof, Brecon Beacons, Wales: Three Caves, One Valley, 8°C Throughout
The Swansea Valley in Powys is home to one of Britain’s most extensive publicly accessible cave complexes. Dan yr Ogof, Cathedral Cave, and Bone Cave sit within a half-mile stretch of the River Tawe valley, each cut through the same limestone formation by glacial meltwater at the end of the last ice age. All three hold between 8 and 10°C throughout the year.
Cathedral Cave takes its name from the scale of its main chamber, which rises 42 metres in height. The silence and the cool grey light under the limestone arch make the space feel constructed rather than natural. Archaeologists excavating Bone Cave in 1938 found the remains of over 40 individuals alongside Bronze Age artefacts dated to around 2,000 BC.
The site opens from late March through October. The car park serves all three caves, and the full visit, covering all three tours, takes around three hours.
Where to Stay: The Castle Hotel, Brecon. A Georgian coaching inn in the town centre, 30 kilometres north of Dan yr Ogof.
Worth Knowing: Dan yr Ogof is the longest cave system in Wales at over 17 kilometres of surveyed passage. The sections open to visitors represent a fraction of the total. The rest is accessible only to trained cave divers who have been exploring extensions since the 1960s.
Smoo Cave, Durness, Sutherland: The Sea Cave at the Top of Britain
Britain’s northernmost accessible sea cave sits at the head of a narrow coastal slot in the limestone cliffs of Sutherland, a few hundred metres from the village of Durness. Smoo Cave is large enough to walk into. The outer chamber measures 15 metres wide and 12 metres high, is open to the sea, and is flooded twice a day at high tide. The inner chamber, reached through a low archway, contains a waterfall dropping through a collapsed section of the cave roof from the moor above.
The cave runs 60 metres into the limestone cliff. The Atlantic air feeding in from the sea and the stone mass above keep the interior consistently cool on even the warmest summer days. The walk down from the car park takes three minutes.
At this latitude in June, the sun does not fully set. The pale light that comes off the Atlantic at 10 pm, combined with the cold air rising off the sea, makes the cave entrance at Smoo a different experience from any cave site in southern Britain.
Where to Stay: Smoo Cave Hotel, Durness. The hotel overlooks the bay, a few minutes’ walk from the cave; the correct base for anyone on the north coast route.
Worth Knowing: The name Smoo comes from the Old Norse word “smjugg,” meaning a narrow cleft. Viking sailors navigating the north coast of Caithness used the cave as a landmark from around the 9th century. It appears in Norse saga material as a recognised coastal feature.
Cool Places UK: Practical Tips
- Book cave tours before you travel during a heatwave period. Chislehurst Caves and Wookey Hole reach capacity quickly when temperatures exceed 30°C. Check each site’s website the morning you plan to go.
- Bring one light layer, regardless of what you wear on top. Cave temperatures of 8 to 11°C feel welcome after 38°C outside, but cold against damp skin within 20 minutes if you stop moving. A thin fleece weighs nothing and changes the experience entirely.
- The River Test is not a public swimming river. Much of the bank is privately owned. Stick to the confirmed National Trust access at Mottisfont and wade only where access is clearly marked.
- For Wistman’s Wood and Smoo Cave, the AllTrails app carries reliable route files. Neither has signed access from the road.
- Caves on Dartmoor and in the Peak District involve uneven ground and low ceilings in places. Follow the guide and stay on the marked route.
- Combine sites where geography allows. Wookey Hole and Dan yr Ogof are two hours apart. Blue John Cavern and White Scar Cave sit on opposite sides of the Pennines, each worth a separate overnight.
Responsible Visiting
Cave ecosystems are fragile in ways invisible to visitors. Stalactite formations in show caves grow at roughly one cubic centimetre per decade. Touching the rock walls transfers skin oils that can stop calcite deposits from forming and permanently discolour the surface. Keep your hands off the cave walls at every site.
White Scar Cave and Blue John Cavern both restrict visitor numbers to protect the cave atmosphere. If a session is full, do not attempt independent entry. The restriction reflects what the cave can absorb without damage.
At Wistman’s Wood, stay on the path. The wood is a Site of Special Scientific Interest. The lichen and moss covering the boulders take decades to establish, and a single footstep can cause permanent damage.
Reader Q&A
What is the coolest place in the UK during a heatwave?
Underground, Wookey Hole Caves in Somerset and Blue John Cavern in Derbyshire hold temperatures of 11°C and 7 to 10°C, respectively, making them the coldest publicly accessible sites in England. At the surface, chalk streams like the River Test run at 10 to 12°C year-round and give immediate relief by wading in.
Are UK caves cold enough to make a real difference in extreme heat?
Yes. A cave temperature of 10°C and a surface temperature of 38°C represent a difference of 28 °C. The thermal shock on entering is immediate. Most visitors describe the first 60 seconds inside a show cave during a heatwave as the most physically arresting experience they can recall from a day out.
Are these cool places open during the summer?
All the cave sites in this article operate scheduled tours from spring through to October. Wookey Hole, Chislehurst Caves, Blue John Cavern, White Scar Cave, and Dan yr Ogof all run tours throughout the summer. Wistman’s Wood and Smoo Cave are accessible year-round with no admission charge. The River Test access at Mottisfont opens during National Trust visiting hours.
Do I need to book in advance?
For cave sites during a heatwave, yes. Book online before travelling. Chislehurst Caves and Wookey Hole in particular sell out quickly when temperatures exceed 30°C. Wistman’s Wood and Smoo Cave need no booking and have no visitor limits.
Where to Stay
- The Ancient Gatehouse Hotel, Wells, Somerset. A 15th-century gatehouse on the Cathedral Green, ten minutes from Wookey Hole.
- Ye Olde Nags Head, Castleton, Derbyshire. Stone-built inn in the village centre, walking distance from Blue John Cavern.
- Springfield Guest House, Ingleton, North Yorkshire. A short walk from White Scar Cave, with views of Ingleborough.
- The Greyhound on the Test, Stockbridge, Hampshire. Riverside Inn on the main street, near the Mottisfont access point.
- Two Bridges Hotel, Two Bridges, Dartmoor. At the foot of the Wistman’s Wood walk, on the West Dart river.
- The Castle Hotel, Brecon, Powys. The Georgian coaching inn is 30 kilometres north of Dan yr Ogof.
- Smoo Cave Hotel, Durness, Sutherland. Overlooking the bay above the cave, the closest accommodation is on the north coast.
Britain was cold for most of its existence, and the rock remembers. Explore more of what lies beneath the surface in the Travel section of Secret Britain.
