The Royal Naval College
Built by Christopher Wren in 1694 as the Greenwich Hospital for the relief and support of seamen and their dependents and for the improvement of navigation. It became the Royal Naval College in 1869. In 1999 the University of Greenwich moved in, and was joined by Trinity College

Built by Christopher Wren in 1694 as the Greenwich Hospital for the relief and support of seamen and their dependents and for the improvement of navigation. It became the Royal Naval College in 1869. In 1999 the University of Greenwich moved in, and was joined by Trinity College
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