Only the walls of Fukuoka-jō (Fukuoka Castle) remain, but the castle's hilltop site (Maizuru-kōen) provides good views of the city and great views of aircraft landing at nearby Hakata airport.
Ōhori-kōen, an expansive park and pond (once part of the castle's moat system) is just adjacent to the castle grounds, and has the traditionally styled Nihon-teien. It's a more recent construction (1984) around a pond with stone gardens and a teahouse.
Nearby, the Fukuoka Art Museum has ancient pottery and Buddhist guardians on one floor; works by Basquiat, Brancusi, Rothko and Warhol upstairs; and galleries pairing Western artists with Japanese contemporaries. Most exhibits change every few months.