Dan yr Ogof Caves
Dan yr Ogof is a 15km long cave system in south Wales, and is the main feature of a show cave complex (advertised as The National Showcaves Centre for Wales) which is claimed to be the largest in Europe.
The cave was first explored by two brothers in 1912, Tommy and Jeff Morgan, using candles and primitive equipment. Completely unsure of what they would discover, they armed themselves with a revolver.
The Morgan brothers' initial expedition was halted at a large lake, which they later managed to cross by coracle. They eventually crossed three more lakes in the manner, but were stopped by a tight crawl.
The squeeze was eventually passed by Eileen Davies in 1963, a member of Swansea University Caving Club.
Exploration has been steadily continued by later cavers who have extended the cave to its present 15km length. Some of this length was reached through cave diving. One of these explorers was Martyn Farr, who wrote a book about the system (see below) in which he claims that the system will eventually be extended to at least 150km.
In a 2005 poll of Radio Times readers, Dan yr Ogof was named as the greatest natural wonder in Britain.
For more information see: http://www.showcaves.co.uk