Tidbinbilla Nature Reserve is a 54.5 square kilometres (21.0 sq mi) nature reserve, on the fringe of Namadgi National Park, that is a short drive from the city of Canberra, in the Australian Capital Territory, the capital city of Australia. The reserve consists of a large valley floor, the Tidbinbilla Mountain and the Gibraltar range. The sides of the valley are steep and relatively undisturbed; the lower slopes are partly cleared and have a history of Aboriginal and European use. Tidbinbilla Mountain is believed to have been used for initiation ceremonies.