Imogen Furlong, Ben Lovett and an unsuspecting Australian climber Ben Stone headed to North Wales to do the Croesor to Rhosydd through trip and check out if all the stories of underground adventure are true…and…well…they are! Prepare yourselves for a real life Indiana Jones trip and its here in Britain!

Armed with the epic write up of a July 2006 trip by Miles Moulding, printed off the Internet we set off into Croesor mine. To be honest this place is more like an underground quarry than a mine. The caverns inside are absolutely massive. At a guess 50m high by 30m wide and these caverns are stacked on top of each other throughout the levels. Situated beneath Moelwyn Mawr there is no doubt

that it’s a hollowed out mountain.

The mines shut down in the 1930’s, after around 100 years of operation. In total they employed approximately 500 men and produced in excess of 11,000 tons of finished slate per annum.
Rhosydd has lain abandoned now for 70 years. Croesor was used as an explosives store up until the late 1970’s and has lain abandoned for the last 30 years.

Exploring these slate mines is a relatively serious undertaking. There is a considerable risk of collapse. We were pretty cautious and refrained from “Whooping” in the chambers, despite the tempting acoustics! Rhosydd suffered a major collapse in the late 1990’s, which destroyed the main underground incline.

Both mines are arranged on 14 separate levels and jointly sport well in excess of 200 chambers, they are undoubtedly some of the biggest slate mines of their era.

This trip navigates a series of obstacles and collapses in between the two mines and is a fantastic journey. The trip starts by gaining the old incline in Croesor climbing up and over the debris where the winding machinery used to be and enter Chamber 1 East.

Croesor’s Chamber 1 East is enormous, possibly the biggest underground chamber in the slate industry. It was several chambers that were worked away into one dark void. This meant that the roof simply couldn’t support itself and collapsed. On insitu ropes, which were in very good condition, we descended down an 80ft pitch into the chamber and picked our way across the huge chunks of slate on the floor of the chamber to other pitch. Again in situ ropes aided the decent (70ft). Rope protectors need to be carefully replaced.

In 2005 some zip wires were put into this mine, creating an absolute thrilling trip. IN real Indiana Jones style, we used the superfast double pulleys to really hammer down ‘Bethan’s Zip’ the zip wire which runs downwards from the base of Chamber 1 East across a deep pool.


Many bridges span the top of these chambers, allowing passage from one tunnel to the next. They must be around 100 years old and now nothing but rotting pieces of timber and quite frankly could collapse at anytime. It is important here to be careful WHAT you clip into as if you clip into something attached to the bridge itself – if it collapses it will drag you down with it to a watery end. There is a plentiful supply of insitu safety lines; it is just a matter of taking care.

One such bridge labelled the “Bridge of Death”, is particularly exciting! It’s not really much of a bridge for a start. Two old tram rails, which bow under your weight, are suspended between two rotting wooden beams. Half way across the bridge runs out…

…from this mid point there is another zip wire, with difficulty I attached myself to a pulley and slid across to the far side. It’s quite tricky technically and requires a combination of strength and confidence.
I got across without too much difficulty but then in sending the pulley back to Ben Stone – I realised I hadn’t weighted it enough and it got stuck half way between us.
GROAN!!! What do we do now?
Well, we both tried reaching out to grab it, but that didn’t work.
After a bit of faffing about, I took the plunge and rescued the thing ‘Stallone’ style by getting a sling and hand over handing across the void to retrieve it. Needs must and it was a real case of putting fear on the back seat!

Everyone across we continued the journey through the mountain.
Croesor and Rhosydd were mined from opposite sides of the same hill. Towards the end of their life as active mines, the underground workings of each slowly approached the other at their extremes. The mine owner’s accused each other of cutting chambers into the others slate.

To resolve this dispute a short tunnel was driven thorough to connect the two and survey the boundary. It was discovered that both mines were guilty of trespassing onto the others side and stealing slate.
The mine owners decided to keep the tunnel between the mines open, in order to increase the ventilation at far end the mines. However, workers from both mines craftily started to use the opposite mine as an opportunity to knock off work early. So the owners then built a wall to stop this from happening. Spoil sports.
That wall is now down and hence the through trip in one mine and out the other is possible.
Both mines are deeply flooded. More than half of Croesor and more than a third of Rhosydd are now below the water level. Many of the flooded sections are 180 foot in depth and yet the water is crystal clear. It is also icy cold. It’s obviously not possible to explore these flooded caverns without diving equipment.

We wore buoyancy aids to ensure that if we did fall into the water, we would at least float.

The largest of these chambers called the “Chamber of Horrors”. Here, there is a short abseil into a dingy is required. You paddle across a lake for about 50m.

Above you hang the remains of a very dodgy looking bridge, bits and pieces precariously still attached to the ceiling. It’s a rather abstract experience.

A short amble through some tunnels and up a slope and we emerged the other side into a Twll (or Pit). It was dark, it was raining, and there was VERY POOR visibility. Due to mist we could only see 2m in any direction. Our head torches reflected back the light straight at us.

The sides of the Twll were slabby and slippery and in places very loose. It was treacherous. It took us an hour and a half to find a suitable route out of the Twll. I tried one way and the hillside basically collapsed onto me.

After finally climbing out and Ben Lovett used micro navigation techniques with OS Map and compass to find our way back across the hillside to the cars.