Ogof Hesp Alyn (Welsh for: Dry Alyn Cave) was discovered by North Wales Caving Club in 1973 in the Alyn Gorge near Cilcain, Flintshire, Wales. Reaching the end of the cave is a serious commitment involving 24 pitches and the draining of two sumps. The proliferation of short, awkward and muddy pitches appear best suited to be tackled by wire ladders, but in the 1980s a team of divers from the Wessex Caving Club who passed the sumps, concluded that single rope technique was preferable, avoiding the need for excessive numbers of people to carry the equipment. A perpetual siphon has since been used at the first sump which does a good job of keeping the water level relatively low, when working properly.