20 sites · down to 90 m · 2 suitable for an intro team
Cave and mine diving in South Wales and Mendip
- Sites20
- Max depth90 m
- Water temperature4–10 °C
- Dive centres4
Now in South Wales, Forest of Dean and Mendip (Great Britain)
- WarningPorth yr Ogof
Diving and fills
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Fills nearby
- Fill stationThe Lake (Cromhall Quarry)Air (232 and 300 bar), nitrox (22–100 %), oxygen and 'mixed gas'; which mixes exactly is not stated — askRoute ↗
- Fill stationCardiff ScubaAir 232 and 300 bar, nitrox up to 99 % (partial-pressure blending), trimix; no booster pumpRoute ↗
- Fill stationVobster QuayAir, nitrox 32/36/50/80 % and 100 % O₂, trimix 21/35, 18/45 and 10/70; max 230–232 bar (no 300 bar)Route ↗
Why come here
Between the Brecon Beacons and the Mendip Hills lie sumps and flooded mines with a long British tradition: Wookey Hole, where the first cave dives were made in 1935, the shallow sumps of Porth yr Ogof, the Dinas silica mine and the deep Noxon Park iron mine in the Forest of Dean. In Britain cave diving is a branch of caving: the sumps are dived through the Cave Diving Group, Wookey Hole and Noxon Park are for CDG members only, and almost everything is on private land where you need the owner's permission; Porth yr Ogof and Dinas are the exceptions without formal permission.
Expect cold water, rarely above 7 °C in sumps and often around 4 °C, with 1–2 m visibility as normal. The CDG recommends solo diving in British sumps, with sidemount, helmet and permanent 4 mm lines. After rain Porth yr Ogof turns into a raging river and floods in Wookey Hole leave buried lines and silt banks, so plan around dry weather. Chepstow sits between the two areas.
Don't miss
- Porth yr Ogof: one of the few British sumps suited to a two-diver team, usually with clear water but at times very strong flow; the Resurgence Pool is off limits to everyone.
- Dinas Silica Mine (Upper Dinas): large chambers in a pillar-and-stall mine with water around 7 °C and usually very good visibility, even after bad weather; according to UKMC, Martyn Farr called it arguably the finest mine dive in the British Isles.
- Wookey Hole: the birthplace of cave diving, where the first dives took place in 1935, open to CDG members only and always dived solo.
- Noxon Park Iron Mine: openworks, caverns and flats with traces of more than 2,000 years of mining and very good visibility, for long and deep dives by CDG members.
On a rest day
- Chepstow Castle: Built on limestone cliffs above the Wye from 1067 or shortly after, it is described as the oldest surviving post-Roman stone fortification in Britain.
- Tintern Abbey: The ruins of the first Cistercian abbey in Wales, founded in 1131, on the River Wye in the valley near Chepstow.
- Cheddar Gorge: A gorge up to 137 m deep on the southern edge of the Mendip Hills, with the show cave of Gough's Cave; the roughly 9,000-year-old skeleton of Cheddar Man was found in its caves.
- Wookey Hole Caves: Walk dry through the show cave past the stalagmite known as the Witch of Wookey, to near the point where the Axe comes out.
All 20 sites
5 closed not shown ·
| Site | Max depth | Type | Certification |
|---|---|---|---|
| Ashwick Grove RisingsPermission neededNot known yet · Full cave | – | Not known yet | Full cave |
| Conning Tower Cave (Balch Cave)Permission neededNot known yet · Full cave | – | Not known yet | Full cave |
| Dinas Silica Mine (Upper Dinas)Permission neededBackmount · Intro to cave | 23 m | Backmount | Intro to cave |
| Hillier's Cave / Hillwithy CavePermission neededNot known yet · Full cave | – | Not known yet | Full cave |
| Little Crapnell SwalletPermission neededNot known yet · Full cave | – | Not known yet | Full cave |
| Mangle HoleNot known yet · Full cave | – | Not known yet | Full cave |
| Manor Farm SwalletPermission neededNot known yet · Full cave | – | Not known yet | Full cave |
| Noxon Park Iron MinePermission neededSidemount · Full cave | 50 m | Sidemount | Full cave |
| Pierre's PotNot known yet · Full cave | – | Not known yet | Full cave |
| Porth yr OgofSidemount · Intro to cave | 7 m | Sidemount | Intro to cave |
| Pwll-y-CwmSidemount · Full cave | 23 m | Sidemount | Full cave |
| Rodney Stoke Rising (Springhead Rising)Permission neededNot known yet · Full cave | – | Not known yet | Full cave |
| St. Dunstan's Well CaveNot known yet · Full cave | 6 m | Not known yet | Full cave |
| Swildon's HoleNot known yet · Full cave | – | Not known yet | Full cave |
| Wookey HolePermission neededSidemount · Full cave | 90 m | Sidemount | Full cave |
Certification requirements, configurations and trimix depths are estimates for planning. Always check them locally and dive within your training.
Map
Dive centres and fill stations
4 dive centres, fill stations and instructors
Fill station
The Lake (Cromhall Quarry)
Cromhall Quarry, Wotton Road, South Gloucestershire GL12 8AA
- Air, nitrox, oxygen and 'mixed gas'
Fill station
Cardiff Scuba
29 Castle Drive, Dinas Powys, Vale of Glamorgan CF64 4NP
- Air 232 and 300 bar, nitrox up to 99 %, trimix
Fill station
Vobster Quay
Upper Vobster, Radstock, Somerset BA3 5SD
- Air, nitrox 32/36/50/80 % and 100 % O₂, trimix 21/35, 18/45 and 10/70
Independent instructor
RebreatherPro Training (Dave Gration)
Works in: United Kingdom, Lot, Malta and Finland (based in Leicestershire)
- Cavern, Intro to cave, Full cave, Sidemount, CCR, Trimix · TDI, IANTD, RAID · Listing at the agency ↗
Order: partners first, clearly marked as partner; then dive centres by distance from Chepstow and independent instructors by name. Not a recommendation: check what they offer yourself.
On this list, or should you be? Get a free partner card →Where to stay
Find a place near Chepstow, Glynneath, Abergavenny, Coleford, Wells
Villages that work well as a base for the caves in this region. Find a place for your team:
- ChepstowBooking.com ↗
- GlynneathBooking.com ↗
- AbergavennyBooking.com ↗
- ColefordBooking.com ↗
- WellsBooking.com ↗
The links to Booking.com are affiliate links: if you book through one, DiveTripPlanner earns a small commission. You pay the same.
Practical info: rules, fills and emergency numbers
Emergencies
- 999 or 112. Accident in a cave or mine: call 999, ask for the police and say it is a cave rescue. Diving accident on land: National Diving Accident Helpline 07831 151 523 (24 h, England and Wales) or the nearest BHA chamber; DAN Europe +39 06 4211 5685.
- Chambers (the BHA list has none in Wales): DDRC Healthcare, Plymouth Science Park, Research Way, Derriford, Plymouth PL6 8BU, tel. 01752 209999, category 1 (~2 h 30 from Chepstow). Midlands Diving Chamber, Hospital of St Cross, Barby Road, Rugby CV22 5PX, tel. 01788 579555, emergency 07931 472602, category 2: no critically ill patients (~2 h).
Access and rules
- Access: almost all British cave-diving sites are on private land and you need the owner's permission; the Cave Diving Group (CDG) knows the current arrangements. One careless visit can close a site for everyone.
- CDG: the British cave-diving club, with a Somerset Section and a Welsh Section. Only CDG members dive in Wookey Hole and in the caves and mines of the Forest of Dean (Noxon Park). Make first contact through a CDG member or via 'Cave Access' on the CDG contact form. Exceptions to the CDG route: Porth yr Ogof (no permit needed; the National Park Authority manages the entrances and the car park), Dinas (no formal permission needed according to TDI; owner Natural Amenities Ltd).
- Insurance: BCA membership (caving member £32 a year) includes public liability insurance. FoDCCAG issues Forest of Dean permits to BCA members only (permits@fodccag.org.uk).
Gas and fills
- Gas: Vobster Quay (air, nitrox, trimix, O₂; max 232 bar) and Cardiff Scuba in Dinas Powys (air to 300 bar, nitrox up to 99 %, trimix with at least 3 hours' notice). No trimix fill station is known in the Neath valley itself: bring O₂ and diluent.
Water and season
- Water and visibility: in sumps rarely above 7 °C and often around 4 °C, with 1–2 m visibility normal and 3–4 m exceptional (CDG); InDEPTH gives an average of 7–10 °C. The Dinas and Noxon Park mines are ~7 °C with usually (very) good visibility.
- Floods: Porth yr Ogof turns into a raging river after rain; in Wookey Hole floods leave debris, buried lines and silt banks.
Safety
- Cave diving in the UK is a branch of caving, not of sport diving. The sumps are dived through the Cave Diving Group (membership and training). These pages are not an invitation to go on your own.
- British practice: the CDG recommends solo diving in British sumps because no British sump allows unimpeded buddy diving; expect many branch lines (in one example 10 in the first 500 m). Sidemount, helmet, hand-held lights and permanent 4 mm lines are the norm.
Rest day
- Non-diving day: Porth yr Ogof is also a popular dry caving trip (over 30,000 visitors a year); below its exit lies the Blue Pool, a small lake fed by rapids, and downstream an attractive walk passes several waterfalls. Wookey Hole is a show cave.
Good to know
- Inland dive centres: NDAC near Chepstow closed permanently on 18 February 2022; the NDAC quarry near Ammanford (124 m deep) is for training organisations only. Vobster Quay (Somerset) is an open quarry to -36 m, members only; non-members on Tuesdays 8:00–15:00 after registering.
News
News articles that mention one of the caves in this region, collected automatically and not checked by us.
Access and rules change: check what applies locally right before your trip. Source: GDELT Project and the news feeds of diving magazines.
Searched automatically, last on 13 Nov 2026.
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