The Kōbōyama tomb mound is one of the oldest and largest keyhole-shaped kofun in eastern Japan, dating from the late 4th century. The mound is 66 metres long and rises 8 metres above the surrounding ground, with a stone chamber that produced an early bronze mirror among other goods.
It sits in a quiet park about 3 km south of the city centre and gets few visitors — a good escape from the castle queues on a busy spring weekend. Reached on foot or by short bus ride.