Crescent Cave description

Description credits

Mark "Tarquin" Wilton-Jones, of Morgannwg Caving Club and Brynmawr Caving Club.


Last updated: 10-Jun-2017


Trefil, South Wales, U.K.

675 metres
81 metres
Entrance grid reference
SO 12977.33:15062.21
Entrance altitude
540.84 metres

A difficult cave to find, particularly in bad weather. It is best to park in the village of Trefil and walk along the road from there, as there is a barrier that blocks the road when the quarries are not operating - cars may be locked in. From the village of Trefil proceed north for about 1.5 km from the Tafarn Ty Uchaf. At this point, a track doubles back on the right and the poorly defined path to the caves heads up the hill to the right from the track junction.

Crescent Cave is most easily found via Chartists Cave, this being somewhat more obvious.

Chartists Cave will be found 1.5 km away (compass bearing 070), about 100 m higher up, just to the south of the highest point, in a south-west facing outcrop between 5 m and 10 m high. The most obvious landmarks on the route to the Chartists Cave are a large cairn to the left (north-west) early on and a large lake called Llyn y Garn Fawr 300 m to the south-west of the entrance (to the right) with a further large cairn overlooking it. Crescent Cave is situated about 200 m SE (compass bearing 130) of Chartists Cave. Look for two streams which sink in a doline complex. The scaffolded entrance is in a subsidiary collapse at the side of a larger doline with the combined streams entering. After long periods of dryness, the streams can dry up completely and very little water is seen throughout the cave.

A compass is essential when visiting the cave as it becomes impossible to see the way back if there is fog or if it is dark.


No control is placed over access but please respect dig sites.

As of 2016, access was not possible, as the scaffolded shaft collapsed in the entrance area some years beforehand.


No control is placed over use of carbide or smoking of cigarettes in Crescent Cave, but in the interest of conservation, please do not dump carbide - spent or unspent, leave cigarette ash or other litter within the cave.

Flooding Characteristics

No parts of the cave are known to flood but after heavy rain storms or long periods of rain, the streams entering the cave can enlarge significantly. It is advisable not to enter the cave under such conditions or take care afterwards due to the loose nature of the entrance area. Being of a constricted nature, The Lower Streamways can become somewhat hazardous to follow during high water conditions.


B.C.R.A. grade 5c survey has been conducted by the Brynmawr Caving Club (M W-J, I W-J, P W-J, M R). The three pages of the survey may be downloaded and printed (not for redistribution, except with express permission) from this site, or may be purchased in full quality from the Brynmawr Caving Club as part of their 1999 journal.


Despite its modest length, this cave should be considered a serious undertaking, and should only be attempted by experienced cavers.

The Entrance

A descent following the stream leads into a small (ex-crescent shaped) chamber with a scaffolded shaft in the floor. At the bottom of this shaft, some small squeezes enter another chamber with the way on down in the floor through yet another scaffolded shaft. At the bottom, a hole under a boulder reaches the top of a 7 m laddered shaft. The way on from the bottom leads under a small waterfall and through a short scaffolded choke (this contains an awkward Z-bend) to enter a 5 m long chamber in a tall rift. On the other side of the chamber, a rift ahead reaches an aven where a rift at the top and a passage at the bottom both end in chokes. To the left in the chamber, a 'climb' over a small wall and a turn right reaches the top of a short climb which in turn reaches the top of the tight, laddered, second pitch. At the bottom, a loose scaffolded climb reaches the top of the third laddered pitch which is followed immediately by the fourth laddered pitch. This reaches the top of a loose slope. Following this downslope, a rift is passed to the left (see The main Level - Right) before the passage funnels down to reach a rift passage. This is the start of The Lower Streamways Part 1.

The Main Level - Right

The rift to the left part way down the slope reaches a junction with the low but wider 'main' passage. (To the left, see The Main Level - Left). To the right, the main route continues as a gravel floored, fossil stream passage, passing many mud, sand and gravel banks. It varies from crawling height to standing height, passing an alcove to the right with a small passage reaching The Lower Streamways Part 2 at 35 m, followed by an inlet and outlet on the right at 37 m and reaches a choke after 75 m. Just before this, a hole up to the right enters a multi-level junction above the choke.

Up to the left, a small passage doubles back along the 'main' passage for 20 m, with two holes down into it, the first being accessed via a flat out crawl to the left and the second entering the main passage opposite the alcove with the small passage accessing the lower streamways, before it closes down.

Above, in the junction, a rift passage back over the 'small passage' will be mentioned later (see The Upper Level) while one ahead by some straws, also in the roof, enters the chamber above Kelly's Eye (mentioned later). Back and to the right is a 7 m aven reaching The Upper Level, whilst between this and the 'small passage', a short, tight passage contains some immature cave pearls.

Ahead in the chamber are two obvious passages, one above the other. The lower of these enters a chamber with no way on while the one above enters another chamber with Kelly's Eye (a crystal covered block) in the floor and an aven into a chamber above. The chamber above has a connection to the left with the multi-level junction, a short, tight passage to the right at its far side and tall rift above. This rift will be mentioned later. From the Kelly's Eye chamber, a climb ahead reaches a decorated passage which ends at two avens after 10 m. The aven to the right, a few metres before the end can be free climbed with care to reach a rift to the left. This can be followed to an awkward descent to the top of the other aven and a higher level continuation of the passage. The second aven is currently (20/7/1997) rigged with a rope. The continuing passage can be followed for 30 m along a fossil streamway to a small decorated chamber and a very tight passage in the floor to the right. This can be followed for 30 m through some decorated sections of passage (extreme care), mostly very tight, to where the passage enlarges into a tall rift. The floor quickly drops some 8 m into the chamber above Kelly's Eye. Ahead, the rift continues as The Highest Level.

The Main Level - Left

A trench in a sandbank can be followed round to the left, to a low crawl to the right over rocks, into a larger passage. Ahead, continuing flat out reaches a series of avens with a total height of 10 m, while up to the left, the large passage is followed up a steep, loose slope. Back over the top of the way in is The Upper Level while the way on continues ahead under a blind aven, and beside a loose choke. The side of the choke can be followed for about 20 m, through some wide sections, to reach a narrow rift with no way on.

The Upper Level

This begins at its junction with The Main Level - Left as a 5 m diameter phreatic tube with a sand floor and quickly enters a chamber. To the right, a narrow rift, becoming too tight, has a voice connection with the head of the fourth pitch. Ahead - left, a climb up enters a rift passage. To the right, a small passage oxbows to the narrowing rift, while to the left, a well decorated passage passes a hole back to the chamber to the left, and continues past many formations, and some boulder obstacles. The passage has been taped off at a formation just before it drops into the multi-level junction in The Main Level - Right.

The Highest Level

This is best reached by climbing the fixed ladder (08/04/2000) from Kelly's Eye, though bolting spits may be usable if the ladder is not. The passage begins as a clamber over rocks. This quickly reaches a junction with an awkward rift to the left and a low passage ahead. The low passage passes some delicate formations (care) and over many holes down to a lower section of the passage, before it turns a zigzag to arrive at a junction. Back over the zigzag, the awkward rift reenters. Ahead, an inlet passage can be followed for just over 10 m, over a blind pitch and through a short crawl, before it becomes impassable. To the left at the junction an easy climb up leads to the base of a slope of rocks at the top of which is a chamber with some avens. A route up boulders ahead reaches a boulder choke after about 10 m. The furthest aven to the left can be climbed with difficulty to reach a passage through an upper part of the choke to where water enters.

The Lower Streamways

Part 1

The rift from the end of The Entrance series quickly reaches the stream. To the right, this passes through a squeeze at floor level to enter a blind aven with a waterfall, while ahead becomes flat out to reach a point where the stream disappears to the left. Ahead can be followed through a squeeze sized passage for 20 m - now blocked to all but flies, mice and the odd bat - to the base of the 4 m climb in The Lower Streamways Part 2.

Part 2

From the alcove in The Main Level - Right, the small 'Motorway Passage' containing a stream can be followed for 5 m to where the stream sinks in the floor. 15 m further on, the passage reaches a 6 m climb down (ladder in place 08/04/2000). At the base, the choked end of The Lower Streamways Part 1 can be seen down a rift in the floor. A rift leading off back under the route in and about 2m off the floor enters an inlet aven, 4 m off the floor. At the base, the choked passage at the end of The Lower Streamways Part 1 enters from under the route in. The way on ahead is small and passes a squeeze by a rock to reach a somewhat larger section. This slopes down to the head of a 3 m climb. From the base, the way on is to climb up into the tall rift ahead. This quickly lowers to a narrow rift where digging is in operation.


Although the entrance series, Motorway Passage and Kelly's Eye pitches originally had flexible ladders in place, and other avens had handlines, these should no longer be trusted. Visitors should expect to need to bring appropriate ladders, hangers, spreaders and lifelines. Spit belays have not been maintained since the entrance collapsed, and may need to be replaced. Ladders will need to be at least 1 or 2 metres longer than the pitches.

Entrance first pitch7 metres
Aven to choked rift after Z-bend9 metres, bolt climbing required
Entrance second pitch3.5 metres
Entrance third pitch4 metres
Entrance fourth pitch10 metres
Lower Streamways Motorway Passage pitch6 metres
Kelly's Eye aven to Highest Level12 metres, bolt climbing or traversing required to rig ladder
Aven climbs to Main Level Right final loop7 metres for first aven or 7.5 metres for second aven (handline suggested)
Optional Main Level Right final loop to Kelly's Eye 8 metres and 4.5 metres


Whilst every care has been taken in the compilation of this cave description, neither the author nor his fellow cavers can accept responsibility for loss or injury arising from any errors, omissions or inaccuracies in this cave description.

This description is subject to copyright. The copyright resides with the author and some other contributors. You are welcome to download, store, retransmit, print and distribute this document PROVIDED THAT (1) you do not do so for any form of reward, financial or otherwise, and (2) all references to the author are retained or otherwise clearly acknowledged. Any infringement of these conditions is an offence in the UK and also in most other countries.

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©1997-2016 MWJ