The Kingsway tram subway opened in 1908. It had been built using the cut and cover technique. It ran from a portal at Holborn and emerged on to street level underneath Waterloo Bridge. There were two stations which were located at Holborn and Aldwych. Access was by means of stairs from street level. Originally the subway could only accommodate single deck trams but in the early 1930’s the subway closed. The original arched roof was removed and the roadway dropped to allow double decked trams to be accommodated. It was re-opened in 1931. Electricity was supplied through a conduit laid between the running rails. In the mid 1970’s a new entrance and ramp at the Waterloo end was built to allow cars to go under Aldwych after coming over Waterloo Bridge from the South bank. You can still see the northern portal opposite Southampton Row. In the movie, ‘The Avengers’, the northern portal is used as the secret entrance to an underground bunker. Trams stopped running early in in the 1950's. If you want to see the northern portal just head North from Holborn underground station and you will see it.