Planning of the extension of the suburban light rail Holmenkollen Line to the city center started in 1901.

Construction began in 1912, but stopped again in 1914 because the municipality and the company could not agree on the location of the terminal station.

It took five years to select a winner, and this allowed the municipality and company to make a compromise by locating the terminus at Nationaltheatret.

[4] Led by Axel Grenholm,[5] the committee recommended building a branch from the Drammen Line as a tunnel under the city center, allowing all trains would terminate at Oslo Ø.

[7] In 1950, they presented a new report, which recommended that a new route for the tunnel be considered, to ease construction and increase safety.

[11] However, it felt that the tunnel should be longer and intersect with the Drammen Line at a point between Skarpsno and Skøyen, and build a second station at Frogner.

[12] The proposal was presented to the Parliament of Norway on 4 November 1961, along with several other matters related to rail transport investments.

Adjacent to the bedrock is a layer of construction concrete and above the platforms, there are corrugated steel plates to catch drips and to reduce noise.

[23] From 1998, the Airport Express Train would start operating, and more capacity would be needed, both at Nationaltheatret and through the Oslo Tunnel.

[24] Construction commenced in October 1997 and consisted of building 830 meters (2,720 ft) of new tunnel, a new double platform, a larger vestibule, escalators and artwork.

Other art was designed by Bård Breivik and Ole Enstad, including reuse of some of the original vestibule art from 1980, including a green marble wall designed by Katrine Giæver that runs along the hallway leading to the metro station.

[28] Between 2008 and 2012, the Norwegian National Rail Administration performed a major upgrade to the section between Lysaker and Etterstad, including the permanent way past Nationaltheatret.

Among the upgrades are axle counters, mounting of an overhead conductor rail, new switches and new tracks.

The area features escalators and elevators to the platforms, staffed ticket sale, lockers, kiosks and cafés.

Eastwards, these continue past Oslo S and serve the southern part of the Dovre Line until Lillehammer.