The building work took place in several stages. In 1995 the construction of the Tiergarten tunnels began, and this work was finished in 2005 with the completion of the last station tunnel. The tunnels provide four tubes for long-distance and regional services and two tubes in a separate alignment for the U-Bahn, in addition to a road tunnel ventilated by a tower completed in 2004. During its construction, the course of the Spree had to be diverted (1996–1998). Water leaks in the tunnels caused over one year's delay to the construction work.