Tsunozuka Kofun, Keyhole-shaped burial mound in Isawa, Japan

Tsunozuka Kofun is a keyhole-shaped mound 43–45 m long, with a two-tier circular rear section about 28 m across and 4 m high and a lower, shorter rectangular front section facing south, 1.5 m high and 10–15 m wide. A horseshoe-shaped ditch surrounds it, and a single tall cedar grows on the rear mound.

The mound was built in the late 5th or early 6th century and is the northernmost keyhole-shaped kofun yet found, lying about 70 km north of any similar tomb in Miyagi Prefecture. Haniwa were noted from the 1930s, and in 1947 it was confirmed as a keyhole-shaped tomb. It became an Iwate Prefectural Historic Site in 1957 and a National Historic Site in 1985.

Local legend says the mound holds the horns of a giant serpent: a wealthy man's greedy wife turned into a snake, and a girl named Sayohime from Matsuura subdued it with Buddhist sutras. Because of this, people believed touching the mound brought a curse, which is why the burial mound has survived to this day.

The site is best reached by car, especially when traveling from the nearest train station, as the drive takes about 15 minutes. Having a vehicle makes it convenient to reach the location and spend more time exploring the grounds.

Local legend says the mound holds the horns of a giant serpent: a wealthy man's greedy wife turned into a snake, and a girl named Sayohime from Matsuura subdued it with Buddhist sutras. Fear of a curse kept the mound intact. A single tall cedar was later planted on the rear circular tier.