sections of Marble Arch Cave underwent development to improve accessibility in order to accept tourist visitors. As well as concrete pathways, safety barriers and electric lighting, this involved installing weirs and jetties for boat access to enable visitors to enter the caves by the same route that Martel and the early explorers took. The development also included boring a new entrance shaft into Skreen Hill and, significantly, excavating a corridor using quarrymens' plugs and feathers, instead of potentially damaging explosives, through the short section of rock separating Pool Chamber from New Chamber. This connected Skreen Hill all the way to The Junction for walking visitors for the first time. At this time, all known entrances to the cave system were gated to allow show cave management to control access. From then on, cavers were only allowed access by agreement with the show cave. The showcave has since become established as a leading tourist attraction and also offers education experiences for schools. It is well regarded internationally for its quality of interpretation and for its approach to the conservation of the cave environment. 1995: Cradle Hole tragedy Three cavers died on a trip into Lower Cradle Hole on 15 January 1995. They were in a group of ten cavers, mostly students from University College Dublin and Dublin Institute of Technology caving clubs, when the three were swept away by fast running water and drowned in the low air-space (or "duck") section of passage between the end of Lower Cradle Hole and the Grand Gallery in Marble Arch Cave. Those killed were Philip Marshall (20), Brian Patrick Kennedy (22) and Conleth Cormican (21). 2009–2010: diving connections In 2009 and 2010 diving connections were made to nearby cave systems by Artur Kozłowski. Kozłowski made the first connecting dive to Prod's Pot – Cascades Rising, doubling the total length of the system from . Subsequently he and Chris Jewell connected the newly established Monastir Sink – Upper Cradle system, extending the Marble Arch system to . The discoveries make this the longest cave in Northern Ireland. Hydrology and development The Marble Arch Cave system is chiefly formed from three rivers which drain off the Marlbank area on the north side of Cuilcagh mountain. From west to east, these tributaries are the Sruh Croppa, the Aghinrawn (or Monastir) and the Owenbrean. The Prod's Pot – Cascades Rising section of the system (connected to Marble Arch