In reply to A Random Climber:
And... yesterday I went off to confirm the tunnel was infact the Arse Hole of Twll Mawr.
Torches on, we quested a hundred metres into the mountain moving though an old wooden doorway in the eerie light-green slate tunnel. We were met by an area of purple slate scree material baring the way. Our day was done - the bottom entrance into Twll Mawr was blocked.
Or so we thought...
Returning to the light, we noticed a clump of silver birch on the level above. A loose and tricky scree scramble took us there only to find a hidden tunnel behind the trees. Was this it? A similar distance to the last tunnel and we were met by another wall of purple slate consistant with the stuff at the bottom of Twll Mawr... only this time there was a tiny hole and light. We'd found it. Caving-style moves on my back, arms through first, scratching my new soft-shell and wiggling my shoulders past the Shelob sized spiders I was born into the pit and I stared up blinking at the line of Supermassive Black Hole.
We'd cracked it: the Arse Hole of Twll Mawr had been entered. Those over 13st need not apply.