Hill House, Helensburgh

Charles Rennie Mackintosh was the architect of Hill House in Helensburgh which was built in 1902 for the Blackie family.

The dull exterior belies a glorious, mostly white, interior jointly designed by Mackintosh and his wife Margaret MacDonald but you'll have to visit to see that for yourself. The National Trust for Scotland website has some interior photos and details of how you can visit the property.

References:
National Trust for Scotland, Places to Visit, Hill House
Hill House, GreatBuildings.com