Fosen is a peninsula and a traditional district in Sør-Trøndelag in central Norway. It extends south from Nord-Trøndelag and forms most of the western shore of Trondheimsfjorden. Peninsula A peninsula (from Latin paene insula, almost island) is a geographical formation consisting of an extension of land from a larger body, surrounded by water on three sides. ... Norway may be divided into a number of traditional districts. ... Sør-Trøndelag is a county in the area Trøndelag in Norway, bordering Nord-Trøndelag, Møre og Romsdal, Oppland and Hedmark. ... County NO-17 Region Trøndelag Administrative centre Steinkjer County mayor Inger Lise Gjørv Area  - Total  - Percentage Ranked 6 22,412 km² 6. ... The Trondheimsfjord, Trondheimsfjorden, is Norways third longest fjord, 130 km long, in the west central part of Norway. ...