Wilton's Music Hall
Wilton's Music Hall is the oldest Grand Music Hall in the world. Built in 1858 it has had a long and colourful history. Wilton's has been the haunt of Victorian sailors (and their ladies), become a Mission, survived two world wars, being a rag warehouse, being forgotten, becoming

Wilton's Music Hall is the oldest Grand Music Hall in the world. Built in 1858 it has had a long and colourful history. Wilton's has been the haunt of Victorian sailors (and their ladies), become a Mission, survived two world wars, being a rag warehouse, being forgotten, becoming
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