Extreme sports are available, such as bungee jumping, water skiing, and paintballing. There are numerous tracks on the island, where it is possible to ride a bike, go for a walk, or go jogging. Apart from Ada, Belgrade has total of 16 islands on the rivers, many still unused. Among them, the Great War Island, at the confluence of Sava, stands out as an oasis of unshattered wildlife (especially birds). These areas, along with nearby Small War Island, are protected by the city's government as a nature preserve. There are 37 protected natural resources in the Belgrade urban area, among which eight are geo-heritage sites, i.e. Straževica profile, Mašin Majdan-Topčider, Profile at the Kalemegdan Fortress, Abandoned quarry in Barajevo, Karagača valley, Artesian well in Ovča, Kapela loess profile, and Lake in Sremčica. Other 29 places are biodiversity sites.