Seen from south to north, the route of the Citybanan tunnel branches off the  after Stockholm South Station on Södermalm, and continues beneath the bay bottom of Riddarfjärden at Söderström, beneath the islet of Riddarholmen, beneath Riddarfjärden at Norrström, to the new City Station.
From south to north, the route of the Citybanan tunnel separates from Stockholm South Station on Södermalm, then traverses under the bay bottom of Riddarfjärden at Söderström, beneath the island of Riddarholmen, and continues underneath Riddarfjärden at Norrström to arrive at the new City Station.