if you wanna have the best castle experience but dont have enough days. dont waste time on osaka castle, the castle inside doesnt have much to see and supercrowed. Go himeji for 1 day trip instead, the castle is far more impressive, the city is less crowed, organized and beautiful. Amanohashidate is a good place to get away from the crowd as well. i suggest spending 1 or 2 days there. please note that the train seats need to be booked before boarding if you're using a JR pass, no extra charges