The Dollis Brook Viaduct, is a railway viaduct in Finchley, North London. It currently carries the London Underground's Northern line between Mill Hill East and Finchley Central stations and is the highest point on the London Underground above ground level, reaching nearly 60 feet (18 m) in height and comprising thirteen 32 feet (9.8 m) wide segmental arches. The viaduct takes its name from the Dollis Brook which it crosses.

The viaduct was designed by Sir John Fowler and Walter Brydone, chief engineer of the Great Northern Railway (GNR) and was opened with the company's single track Edgware, Highgate and London Railway on 22 August 1867.

In the 1920s, the London and North Eastern Railway (successor to the GNR) planned to electrify the line, but work was not carried out until the 1930s when it was done as part of the London Transport's Northern Heights plan in preparation for a transfer of the line to the Northern line. The start of the Second World War prevented the plans being completed and only the section of the line to Mill Hill East was electrified and reopened by London Transport in 1941. British Rail freight services to Edgware continued on the line until 1964 when it was closed west of Mill Hill East. (Full article...)