The most famous is Himeji Castle, in the city of Himeji. It is so brilliantly white that people call it 'the white heron' - because it looks like a big white bird about to take off. It has six floors and 83 different rooms. Most of the building has been standing for over 400 years.
Japanese castles were built on top of enormous stone bases. The stones weren't cemented together - they were carefully shaped to fit like a puzzle. This 'cyclopean masonry' is so cleverly made that the bases have survived hundreds of earthquakes.
Inside, the castles have winding stairways, hidden rooms and gentle wooden floors that creak when you step on them. Some floors were built to creak on purpose, like a wooden alarm system. They're called 'nightingale floors' because the sound is a bit like a bird singing.
Today, the castles aren't homes anymore. Most have been turned into museums where children visit on school trips. You take off your shoes at the door, just like at a Japanese home, and walk around in socks. Some castles have free 'try on a kimono' days for kids.