Re: King Arthur's Labyrinth
Llechwedd is very safe and tourist oriented. For more of an adventure you can spend a day exploring the nearby Cwmorthin slate mine - look up Go Below Extreme.
You enter the mine in the middle level (the upper levels are all collapsed) and make your way down to the lowest level that's not flooded and back up again. Aong the way you climb up and traverse vertical walls (via ferrata style), zip wire across the top of deep caverns, an abseil descent, ride down the deepest underground zip line, and finally jump of an underground cliff attached to a free fall descender.
There are no concessions to "tourists". The mine is exacly as left, except for the zip wires and safety wires. The only lighting is your helmet torch.