Lyderhorn is a mountain in Bergen, Norway. It is one of "De syv fjell", the seven mountains surrounding the city centre, and the starting location of Bergen Turlag's annual trip of the mountains. It is located by Liavatnet approximately five kilometers west of the city center. Due to its prominent visibility from the seas, it has historically been a navigational mark for sailors. Ørnafjellet (329 metres above sea level) is an adjacent peak, and below Ørnafjellet are the two lakes Skåleviksvatnet and Søre Skåleviksvatnet. North of Ørnafjellet is Kvarven fort, a strategic point during World War II, still featuring several bunkers and cannon positions used in the defense of Bergen.