The Marble Arch Caves are a series of natural limestone caves located near the village of Florencecourt in County Fermanagh, Northern Ireland. The caves are named after the nearby Marble Arch, a natural limestone arch at the upstream end of Cladagh Glen under which the Cladagh River flows. The caves are formed from three rivers draining off the northern slopes of Cuilcagh mountain, which combine underground to form the Cladagh. On the surface, the river emerges from the largest karst resurgence in Ireland, and one of the largest in the United Kingdom. At the Marble Arch Caves form the longest known cave system in Northern Ireland, and the karst is considered to be among the finest in the British Isles. History 18th–19th century: The Junction, Grand Gallery, and Pool Chamber The Marble Arch, Cladagh River resurgence and three large dolines on the plateau above the end of Cladagh Glen were all known well before underground exploration began; in fact the arch was a popular tourist attraction in the 19th century. As early as the 1730s, the Reverend William Henry described these features, as well as the sinks of the Owenbrean, Aghinrawn and Sruh Croppa rivers which he correctly surmised to be feeders of the system. Without venturing far into the cave, Henry descended to the base of one of the dolines above the resurgence: The stream passages at the base of each shakehole were first explored by Édouard-Alfred Martel and Dublin naturalist Lyster Jameson in 1895. Using a canvas boat, and with candles and magnesium flares for light, Martel and Jameson found of passages, including the junction where the three rivers (the Owenbrean and the combined Aghinrawn and Sruh Croppa) meet. They drew a map of the discoveries and line drawings depicting the expedition, noting the upstream conclusion by boat in the Grand Gallery, and on foot at Pool Chamber. Today, this route to Pool Chamber forms part of the walking section of the show cave. Martel and Jameson also investigated Cradle Hole, a very large surface shakehole south-south-west of Marble Arch. A cave entrance in the north-eastern corner—Lower Cradle—was explored, reaching an underground river and passages with the same proportions as those in the Marble Arch Cave. 1907–1908: Great Boulder Chamber and dye tracing In 1907, English cavers from the Yorkshire Ramblers' Club began exploration in the area, and without access to a boat they decided to wade the