Recent heavy rainfall has led to the discovery of a 500-year-old tunnel under parts of the Noord-Holland town of Hoorn, the city council said on Friday.

The rain washed away part of the pavement in a narrow passage named ‘t Glop, just off the town’s main square. Archaeologists investigated the hole and found the tunnel, which had been sealed up.

The tunnel, part of a sewage system leading to the former Zuider Zee, has collapsed in many places but the council hopes to open up parts of it to the public in time for national heritage day in September.

The tunnel runs under the site of a hospital dating from 1563, now home to the Kunstencentrum De Boterhal and certainly predates it, the town council said.