Himeji Castle is the one that survived. Japan has a lot of reconstructed keeps, concrete inside and gift shop on the ground floor, but the big white donjon here is the real thing, largely as it stood in the early 1600s when Ikeda Terumasa rebuilt the place on the hill. It came through the bombing of 1945 and the Kobe earthquake of 1995 with the timbers intact, and it has been a World Heritage site since 1993. The plaster is so brilliantly white that people call it Hakuro-jo, the White Heron, and on a clear morning from the east side you can see why: the roofs stack up like a bird lifting off.
The city around it is big, nearly half a million people, so this is a place for a slow arrival. Come in on the old Sanyo corridor early, park the bike at one of the lots near the station end of the avenue that runs straight to the castle gate, and walk the last stretch. The avenue is wide and dead flat, the castle sits at the end of it like a punchline. Fuel and everything else are in town; you will not be short of anything within a few minutes of the walls.
Inside, the keep is a maze of narrow stairs and wooden floors polished by four centuries of socks, and the defensive design is genuinely clever: winding approaches, hidden gun ports, gates that make you turn sharply under fire. The castle was never actually besieged in anger, which probably explains why so much of it is still standing. Next door is the Koko-en garden, a set of walled gardens in the Edo style, good for twenty quiet minutes if the crowds on the castle stairs have worn you down.
For food, look for Himeji oden, which the locals eat with a ginger-spiked soy dip rather than the usual mustard, and for anago, the sea eel of the Seto Inland Sea, grilled over charcoal. Both are simple things done properly. If you have an afternoon spare, the ridge of Mount Shosha rises behind the city with the old temple complex of Engyo-ji on top, reached by ropeway and a short walk through cedar forest.
Riding out, the Harima plain is flat and busy, with traffic lights and trucks, so the pleasure is in what you stopped to see rather than the tarmac. Spring brings the cherry blossoms around the moat, and November can set the maples on fire; summer is hot and humid enough that the tall white walls feel almost like a refrigerator by comparison.