In reply to joelc:
Hi Joel just a quick response as I'm very busy! Yes the Croesor-Rhosydd Through Trip is certainly only for experienced folks well versed in SRT techniques, and a quick copy and paste, taken from the Croesor-Rhosydd wiki page should be read by all:
"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."