A curious entrance turret
adjacent to the Tower of London
reads "London Hydraulic
Power Company". Its history is interesting and existence incongruous.
The enterance leads to a tunnel under the Thames, 1,430 feet long and 7 feet in diameter, constructed as the first subway line in London by Peter Barlow and James Henry Greathead. Construction began in 1869 and was completed in an astounding 10 months at a cost of £16,000. Construction was done with pre-cast iron segments and syringes of grout.
Initially the tunnel conveyed a 12 person cable towed car. The funicular was operated for only 3 months due to insufficient capacity, and the tunnel was taken over by a receiver. It was operated as a pedestrian tunnel with gas lighting. The construction of Tower Bridge in 1894 rendered the tunnel obsolete, and it was closed in 1896. As the only tunnel under the Thames at the time, it was retasked to carry hydraulic power to the Docklands in the 1920's, was damaged (and repaired) during WW2, and presently houses data and cable television wiring.
The Tower Hill side is clearly visible by the pier enterance. The south shore terminus is on Vine Lane (just off Tooley Street), and is mired in the More London (aka "London Testicle") construction project as of 2001-May. Urban exploration is possible, but late-night access to the Tower Hill side is unrealistic (unless you want the men in black after you). Finding the southern entrance can be a problem. Mind the CCTV on the construction hoardings.