This is probably the least "Mathy" thing I will ever post. In my opinion, it's impossible to have architecture that isn't mathematical in some sense, so I am posting it anyway. Two years ago, I made a papercraft version of a cathedral in Christchurch New Zealand (It was severely damaged in an earthquake earlier this year) and cut holes for all of the windows and lit it with LED lights. I gave it to my Mom as a Christmas gift. I thought it made for a pretty amazing "Christmas Village" piece.
Here you can see the switch on the lower right:
And here is a shot showing the inner workings:
I'd love to see someone make some lighted projects for Christmas. If you do, feel free to post 'em up! Also be sure to check out all of the cool papercraft at the canon site. There is a lot of amazing architectural pieces. I especially love Antoni Gaudi's cathedral Sagrada Familia (template here), and some pretty cool holiday things including some pop up card templates if you search around.