The castle is called Ryūgū-jō and comes from a classical Japanese folktale, Urashima-Tarō. The fact of having a ship modeled after a castle may seem strange, but considering how the medieval Japanese warships (atakebune) were built, like floating fortresses, the design doesn't seem so strange... Plus, the castle from the folktale was owned by Ryūjin, the dragon god of the sea, and was located under the sea.
Travel tip: The Toba Bay Cruise departs nearby the Toba Station, close to the Mikomoto Pear Island. The trip takes about 50 minutes and costs 1700 yen.
EXIF info:
Nikon D90
Lens: 18-70mm F/3.5-4.5G
Focal Length: 38mm
Aperture: F/5.6
Shutter Speed: 1/1250s
ISO Sensitivity: ISO 200