Croesor Rhosydd Through Trip

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Croesor: SH 6567 4556

Rhosydd: SH 6652 4615


This popular and exciting mine trip connects the disused slate mines of Croesor which lies high on the slopes of Cwm Croesor, and Rhosydd which is situated on the watershed of Bwlch Rhosydd between Cwm Croesor and Cwm Orthin.

The normal direction is to enter Croesor and traverse to (and exit from) Rhosydd. Although the traverse would be possible in the opposite direction, this is not to be advised. There are three abseils that would need to be reversed and it would be impossible to inspect the state of the fixed ropes (if indeed they are in place) before using them. As there are many sharp slate edges in this sort of mine using a fixed rope without pre-inspection would be extremely foolhardy.

Due to the dangerous and fragile state of both the mine itself and some of the fixed aids, it must be assumed that parts of this route may become impassable or may change at any time. Past roof collapses have necessitated changes in the route on more than one occasion. That said, over the years the route has become increasingly popular which has led to many of the dangers being sanitized and the quality of many of the fixings such as the zip-wires is excellent.

It is essential that all party members are well-prepared for this trip. All members will need:

  • A reliable light source. The trip will last several hours and your light may become submerged.
  • Warm clothing. The mines can draught strongly and become very cold, especially if you're wet.
  • A helmet
  • SRT knowledge and equipment. You should carry the appropriate equipment and have the knowledge to both descend and ascend ropes. It is not enough to only know how to abseil. You may find your route blocked and need to reverse your path to the entrance.
  • Some means of buoyancy and the ability to swim. At times you may need to swim across flooded chambers and you may fall in from the traverses or from a boat.

Before embarking on this trip you should leave details your trip and a proposed exit time with a third party who will be able to summon the rescue services if you become stranded in the mines.

It is worth noting that if you exit Rhosydd via the upper Twll exit you end up on high terrain. In bad weather it can be difficult to navigate back into Cwm Croesor. It is recommended to take a map and compass/GPS to help you find your way.


Cwm Croesor

Croesor Village car park at SH 6314 4467.

Cwm Orthin

At the end of the road above Tanygrisiau village at SH 6811 4574.


Croesor entrance at SH657457 - photo by Rhys Williams
zipwire - photo by Dan Sandford
First Bridge - photo by Dan Sandford
Second Bridge (now gone) - photo by Dan Sandford
Chamber of Horrors boat crossing - photo by Dan Sandford
West Twll at SH666453 - photo by Dan Sandford
Rhosydd adit at SH665461- photo by Rhys Williams

From Cwm Croesor

From the car park, go back to the crossroads then turn left and follow the tarmac road along the bottom of the valley. Eventually this becomes a 4WD track and climbs diagonally up the southern (right) side of the valley to bring you out at the Croesor workings. The grilled adit entrance is obvious and to your right behind some old buildings. Unless you are familiar with the area, a map will be required to make sure you choose the correct ascending track. Map.

From Cwm Orthin

The simplest route is to follow the 4WD track up through the slate tips into Cwm Orthin. Follow this main track all the way alongside the western (left) side of Llyn Cwmorthin. This track then climbs diagonally up the head of the valley into the Rhosydd slate tips bringing you out at the abandoned Rhosydd mine barracks. The Rhosydd adit entrance is obvious to the left and behind the old buildings. It is at the foot of an incline and usually has water running out from it. The route onto Croesor mine from here is less obvious and follows a footpath across the open mountain, crossing the outflow of Llyn Croesor. This section will require the use of a map and compass/GPS unless you are familiar with the area. Map.

There is a direct route up from Tanygrisiau to Croesor without passing the Rhosydd adit, however, the early section of the footpath is really not obvious on the ground and climbs very steeply indeed. The route takes you over some high ground where the visibility and weather is likely to be worse before you drop down past the Twll entrances and on to the Croesor workings. This route will require the use of a map and compass unless you are very familiar with the area. This route is not recommended. Map.

The Through Trip


The rigging of the various obstacles changes from time to time. This description reflects the rigging at the end of October 2012.

Entrance Series

Pass through the grilled Croesor entrance, and head straight along the adit for about 400 metres. At the end, a short climb up with fixed handlines in place leads to an incline with a large diameter ceramic pipe which ascends to a sturdy grille across the passage. At this point turn left along a level to reach the top of a pitch with fixed ropes.

After carefully checking the state of the fixed ropes, abseil down ensuring that the rope protectors are in place. From the base of the pitch, walk and scramble straight across large collapsed blocks in a massive chamber to reach the second pitch. Again, carefully check the ropes and rope protectors, and descend.

At the bottom scramble down boulders to the start of a descending Tyrolean zip-wire across a lake. Check the condition of the wire. The in-situ fairly heavy industrial pulley gives a stately ride, but if using your own pulley it is essential to employ some kind of braking system on the crossing to prevent hitting the far side at high speed. A spare pull-back cord should also be taken.

Across the lake is a short section of dry passage before another lake is met. The in-situ suspension bridge can be used to cross this, but if it is missing a dinghy or a cold swim would be required. From the large chamber at the other side of the lake go left and follow the obvious passage with some railway tracks to the first bridge.

First Bridge

Walk carefully along the large slippery wooden beam using cows-tails clipped into the fixed ropes for protection, then straight ahead to where the next bridge used to be.

Second Bridge

This is no longer in place, but a traverse line can be followed round the chamber to the right, to reach the passage opposite after a slightly energetic tension traverse.

Third Bridge (The Bridge of Death)

There is a traverse wire which is belayed in the middle, so it is necessary to pass a join. This is best crossed with a pulley (or a steel karabiner) on each section, with a pull-back line.

The Chamber of Horrors

There is currently a canoe and an inflatable dingy attached to a line and a pulley system for towing them across the lake, but take your own just in case. Abseil down and carefully embark your chosen craft. Watch out for sharp rocks at the foot of the abseil. The fixed line can be used to pull yourself across to the far side of the lake. It is advisable to take your own pull back line in case the fixed line is not in place.

At the other side there are fixed ropes leading round a traverse to the bottom of a short pitch up into the continuation of the passage. An old wall with bent iron bars marks the entry into the Rhosydd workings.

To Exit via the Rhosydd Adit

Follow the passage and then go right up the second slippery slope. Turn left at the top and through some boulders to emerge in a chamber where there is a passage with some railway lines and points, with a steep scree slope on the left.

Follow the passage with the tracks past several other scree slopes leading down to the left, and some steps leading up to a dead end on the right. Ignore these and go through another broken wall, and then past the foot of a long incline which leads to a dead end with a counterweight cart half way it.

The passage terminates in wriggle through collapsed boulders, into a chamber. Ascend the boulder slope for a few metres towards daylight, which is the first exit to the Twll. When you can, cross over to the left wall and when this gives out descend the massive chamber. Follow the passage at the bottom past several other big openings to the surface, including one with massive wooden beams in the floor.

Descend a well-used slope on the left for a few metres until you can cross over into a larger, parallel incline on the right. Descend this more easily. At the bottom, continue in the same direction for a few metres to a junction complex. A large adit leads off the left, at the end of which can be seen daylight. The exit is reached after about 650 metres of relaxed strolling.


To Cwm Croesor

If exiting from the Twll, a walk across the open mountain down to the Croesor entrance is best, a map and compass/GPS will be required for this. Then follow the main 4WD track down into the valley. Map.

If returning from the Rhosydd adit, it is possible to turn left and follow a lower footpath into Cwm Croesor without passing the Croesor adit. A map will be required to ensure you hit the top of the path. Map.

To Cwm Orthin

If exiting the Twll, a walk over open mountain and down the inclines to the Rhosydd adit is best. A map and compass/GPS will be required for this. From the Rhosydd adit, follow the main 4WD track to the right and down into Cwmorthin. Follow along the lakeside back to Tanygrisiau. Map.

It is possible to take the direct route from the Twll and over the ridge to Tanygrisiau, however, the lower slopes are extremely steep and the path non-existent in places. A map and compass will be required for this. This route is not recommended. Map.

Suggested Equipment

  • For the cable Tyroleans and traverse lines, a dedicated tandem pulley for use on wires is recommended, such as the Petzl Tandem Cable. Two are required as the wire on the penultimate lake is split in the middle.
  • Every party should aim to carry some spare rope and rigging kit to enable them to complete the trip or escape if the fixed aids are in a bad way or if things go wrong.
  • Although there are usually serviceable dinghies in situ and lots of string to pull them back across the Chamber of Horrors, it is probably essential to take your own just in case (and take it out with you - don't abandon it in the mine!).
  • Wearing gloves is recommended as broken slate can be sharp.
  • A map and compass/GPS is probably essential for finding the entrances and your way home if you're not extremely familiar with the area. This is proper Snowdonia mountain terrain and is often completely covered in cloud!


It goes without saying that you should not leave any litter in the mines, but if you replace any fixed equipment then please take the old gear out with you. This includes things like inflatable boats.

Local accommodation

Lancashire Caving and Climbing Club have a hut in Tanygrisiau right by the walk up to Rhosydd and also Cwmorthin. Well appointed and reasonably priced.

Somewhat further away is a Bunkbarn and campsite in Tremadog owned by the legendary Eric Jones.


"Rhosydd Slate Quarry" by MJT Lewis and JH Denton, ISBN 0 9522979 0 6 contains full surveys of Rhosydd. Although the 5/9 incline has collapsed since the book was published, making the trip from the West Twll to the 9 adit slightly more exciting.

Trip write ups/descriptions

Video clips

There are now numerous video clips of the through trip on YouTube.


"Cartoon" images of the trip by Pete Stockton

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