A cluster of large keyhole-shaped tumuli on the south-western edge of the city, dating to the late fourth and early fifth centuries — the period when the proto-Japanese state was beginning to consolidate. The largest of the mounds, Iwaseoyama Kofun proper, is around a hundred metres long and is one of the most significant surviving tombs of its kind in western Japan.
Quiet, off the tourist circuit, and unsupervised: you can walk over the lower mounds and around the larger ones at any time. Small information panels are in Japanese only. Easy bicycle ride or taxi from the city centre; allow an hour.