Home to numerous museums, temples, and the oldest zoo in Japan, Ueno Park reigns supreme as one of Tokyo’s top tourist attractions. Most likely, any visitor to the city finds themselves walking in this park sooner or later, at least once during their trip.

Once part of the huge temple complex of Kan’ei-ji, the park itself boasts plenty of interesting landmarks, from an abandoned train station to the face-only Great Buddha. There is another unusual attraction hiding in plain sight, where most visitors simply walk past unaware of its existence.

The Suribachiyama tumulus, also referred to as the “Old Tomb on Mount Suribachi” in the description on its historical marker, sits inconspicuously along the paths in Ueno Park leading up to the zoo and the museums. Were it not for the sign, it could easily be mistaken for a regular hill, complete with simple benches on top.

It is, however, a legitimate archaeological site, estimated to be around 1,500 years old. Having been severely damaged throughout its history, no excavation has officially taken place here, leaving it a bit of a mystery. It is apparent, though, that it is a keyhole-type burial mound typical of the Kofun period of Japan, and a handful of pottery sherds have been found at the site.