Clink Prison Museum
A museum that tries to recreate the conditions of the original prison that used to be on this site from the 12th century until 1780, which was notorious the name of it has since become slang as a generic term for prison.

A museum that tries to recreate the conditions of the original prison that used to be on this site from the 12th century until 1780, which was notorious the name of it has since become slang as a generic term for prison.
Check the official site before travelling; hours and prices can change.
More museums

Sir John Soane's Museum
Free, tiny, deranged — Soane's own house preserved exactly as he left it in 1837.

The Wallace Collection
Free national museum in a Manchester Square townhouse — armour, Boucher, the Laughing Cavalier.

The British Museum
Free, vast, civilisationally heavy — go for one room, not all of them.
Source: wikivoyage