Sir John Soane's Museum is a reasonably well know museum, but compared to its close neighbor the British Museum must count as a bit rarely visited. The collection is a miscellany of objects reflecting the original owner, Sir John Soane's tastes. As an architect Soane worked on a number of other buildings, apart from the museum itself, that can be seen around London such as the Dulwich Picture Gallery and Pitzhanger Manor.
My personal highlight from the collection is the Hogarth paintings, with the Election and Rake's Progress being on show here. A pleasing development is more exhibition space is planned with the architectural models due to go back onto public display.
As this museum is at Lincoln's Inn Fields more or less directly opposite the Hunterian museum of Surgery and Medicine it is well worth a trip to Holborn for. The Hunterian will be a subject of one of the entries in this series so that is all I'll add for now.
The Soane Museum is free entry and again I'll encourage visitors to donate or buy items in the shop to help support it.