Goryōkaku is a Western-style star fort built in 1866 — one of the only Japanese fortifications designed on European principles, with five angular bastions intended to eliminate blind spots in the defensive perimeter. The design, influenced by French military engineering, was advanced but came too late: it was completed only two years before the Boshin War battles that would make it famous as the last holdout of the old shogunate.
The fort itself is now a public park famous for its cherry blossoms in late April — the moat and earthworks are lined with about 1,600 trees, and the combination of the geometric earthworks reflected in the moat and the overhanging blossoms is one of Hokkaido's celebrated spring views. The Goryōkaku Tower adjacent to the fort offers a bird's-eye view of the star shape from its observation deck; the ground-level experience from within the moat makes the distinctive geometry much harder to appreciate. A small museum inside the tower covers the fort's history and the Battle of Hakodate in reasonable detail with good English explanations.