Akerselva

From its source at Maridalsvannet reservoir, the Akerselva snakes for 9km down through Oslo until it spills into the fjord behind the Opera House. This fast-flowing river was once the center of Oslo's industry and then, until the late 20th century, abandoned and unloved. Today it's one of the city's favorite places to relax, a swath of forested rapids, waterfalls, running tracks, picnic grounds, swimming holes and fishing spots. The crashing Vøyenfossen (Vøyen waterfall) at Sagene is an inner-urban wonder.