The Minangkabau ethnic group retain a unique matrilineal tradition, despite being devoted Muslims. Other indigenous ethnic teams include the Asmat and Dani in Papua, the Dayak in Kalimantan and the Mentawai in Sumatra, where conventional rituals are still observed. In Sumbawa, Mount Tambora with its historical massive volcanic eruption again in 1815 that produced large caldera also had gained attention among hikers. In the neighbouring island of Flores, the three-coloured volcanic crater-lake of Kelimutu can be hailed as certainly one of Indonesia’s pure surprise and had attracted guests worldwide. Puncak Jaya within the Lorentz National Park, the best mountain in Indonesia and one of the few mountains with ice caps on the equator provides the opportunity of rock climbing. In Sumatra, there are the remains of a supervolcano eruption that have created the landscape of Lake Toba close to Medan in North Sumatra.