While on our brief visit to Kyoto, we explored Nijo Castle. There was a lot of historical information about it, and the outsides of the building in particular were very impressive. My favourite feature, though, was the nightingale floor - an early line in burglar alarms (and anti-ninja technology) as it was supposed to be impossible to walk across the floor without being heard. (A clever arrangement of nails and squeakly clamps under the floor make it 'sing' as you step on each board). There were some pretty ornate carvings outside too.
