"Sarah Siddons, the last operational Metropolitan Railway electric locomotive, will make a special visit to the Depot for the Open Weekend. Built in 1921 and capable of running on the Underground, the No. 12 'Sarah Siddons' is one of twenty locomotives built by Metropolitan Vickers in 1921. Each was later given names of real or fictitious people associated with the area served by the Metropolitan Railway. 'Sarah' was retained beyond 1961 - when most of the other locomotives were retired for shunting, brake block testing, and latterly for special passenger trains."
Also "large or small, scenes are depicted right down to the finest detail and cover all modes of London travel from Underground trains and trams to cycling and walking."
Opening times: 11.00 - 17.00 (Last admission 16.00). London Transport Museum's Depot is located opposite Acton Town Station at 118 - 120 Gunnersbury Lane, London W3 8BQ. Unfortunately as Crash Calloway points out in a discussion why "TFL/LT/LU in their infinite wisdom would close both the District and Piccadilly Lines up to Acton Town over this weekend". So if travelling by public transport you will need to use the replacement bus service.
Admission (tickets valid both days): Adults £8.00, Concessions & senior citizens £6.50, accompanied children under 16 go free. For full details click here.
Here's a report from the last time I went. Have fun.