On our way back from Weybridge we called in at Calke Abbey in Derbyshire.
http://www.nationaltrust.org.uk/main/w-calkeabbey
It is very dark inside so that items already damaged no longer deteriorate.
This property is very unusual in that it has not been fully restored, only made structurally safe. Many of the rooms have been left exactly as they were found 25 years ago when the house was virtually derelict.
Many of the rooms are just as the owner left them, full of a jumble of items that were no longer used.