The Jenolan Caves are limestone caves located within the Jenolan Karst Conservation Reserve in the Central Tablelands region, west of the Blue Mountains, in Jenolan, Oberon Council, New South Wales, in eastern Australia. The caves and 3,083-hectare (7,620-acre) reserve are situated approximately 175 kilometres (109 mi) west of Sydney, 20 kilometres (12 mi) east of Oberon and 30 kilometres (19 mi) west of Katoomba. Dating back to 340million years ago, it is the oldest known and dated open cave system in the world.