In 1912, the construction of the first underground railway in the Nordic Countries started, when A/S Holmenkolbanen started construction of an extension of their line from Majorstuen to Nationaltheatret; the 2 kilometers line was opened in 1928 (and was then only the second underground railway to be opened in the Nordic countries after Boulevardtunnlen in Copenhagen which opened in July 1918 ), with one intermediate station at Valkyrie Plass, giving the two suburban lines access to the central business district of Oslo.