If you're glad Christmas comes but once every 365 days, then stay well clear of the Käthe Wohlfahrt Weihnachtsdorf, a Yuletide superstore that also houses this Christmas Museum. This repository of all things 'Ho! Ho! Ho!' traces the development of various Christmas customs and decorations, and includes a display of 150 Santa figures, plus lots of retro baubles and tinsel – particularly surreal in mid-July when the mercury outside is pushing 30°C.
Not as big a hit with younger kids as you might predict, as they can't get their hands on anything.