The view from the castle is nice, and it's very easy to get to (especially with the car park right at the base of the castle).
The interior is sparse, just concrete walls, but it has some interesting pieces about the Christian history from the region
No. The current five-story keep is a 1964 concrete reconstruction. The original castle was dismantled in the late 19th century during the Meiji period. The stone walls and moat system are original and remain from the Edo period structure.
The keep contains a museum displaying artifacts from the Shimabara Rebellion, including weapons, armor, and historical documents about Christian persecution. The upper floors provide observation decks with views of Shimabara city, the Ariake Sea, and Mount Unzen. The grounds include the original stone walls, water-filled moats with koi, and Japanese gardens.
The castle grounds are free. Admission to the main keep museum is 550 yen for adults, with reduced rates for children and students.
From Nagasaki, take the JR Nagasaki Main Line to Isahaya Station, then transfer to the Shimabara Railway. Total travel time is approximately 2 hours. From Shimabara Station, the castle is 2 kilometers away—accessible by a 5-minute bus ride, taxi, or 25-minute walk. Ferry services from Kumamoto are also available.