Goryokaku is only one pengtagon-shaped castle ruin present in Japan.  In the end of Edo-period, the Edo gavenment made this fort to enhance the defence ability of Hakodate.   The Goryoukaku tower has been built nearby Goryokaku.  One can see the whole pentago shape of the fort only when going up to the top of the tower.  The original tower of 60 m high was located just adjacent to the tower.  The 2nd genaration 90m-high tower, which we see in the photo, was built in 2006.