Daisen Kofun — Emperor Nintoku's Keyhole Tomb (5th Century)

Daisen Kofun (大仙古墳), also known as Emperor Nintoku's Tomb, is the world's largest tomb by area — a 486-meter keyhole-shaped (前方後円墳) burial mound from the 5th century CE. The tomb is surrounded by three moats and forests, creating a 47-hectare complex visible from above as a distinct keyhole shape. The tomb is a UNESCO World Heritage Site (2019) as part of the Mozu-Furuichi Kofun Group.

The tomb's interior is sealed and has never been archaeologically excavated (Imperial Household Agency prohibits excavation of imperial tombs), leaving its contents and exact construction date mysterious. Visitors cannot enter the tomb grounds but can walk the perimeter and view from observation platform.