The tunnel replaced an expensive and sometimes unreliable ferry service, and was intended to allow workers living on the south side of the Thames to reach their workplaces in the London docks and shipyards then situated on the Isle of Dogs.
The entrance shafts at both ends lie beneath glazed cupolas, with lifts (installed in 1904, upgraded in 1992) and spiral staircases allowing pedestrians to reach the sloping, tile-lined tunnel at the bottom. The cast-iron tunnel itself is some 1,200 feet (400m) long and has an internal diameter of about 9 feet (3m). Its cast-iron rings are lined with concrete which has been surfaced with some 200,000 white glazed tiles.
The tunnel is a convenient link between Greenwich town centre - the entrance is close to the preserved tea clipper Cutty Sark - and Island Gardens, a park with excellent views across the river to the former Greenwich Hospital, the Queen's House and the Royal Greenwich Observatory.
The tunnel is classed as a public highway and therefore by law is kept open 24 hours a day. However the lift service is only operated during periods of high demand. Ironically (because cyclists are not allowed to ride through the tunnel), it is also part of the UK's National Cycle Network, Route 1, linking Inverness and Dover.