Behind today's advent door is a whole museum! The Geffrye Museum is one of my favourite in London - it is dedicated to the history of British domestic interior design and each period is reflected through a staged room. At Christmas, every room set is dressed in seasonal decorations appropriate to the period:
Miles and I last went in Christmas '05 and it was lovely. If you visit their website they have a virtual advent calendar which showcases seasonal items from their collection. I heartily recommend a real visit to the museum too, and the exhibitions are wonderful at any time of the year!