Visitors to Lindisfarne Priory had to be evacuated when a suspected bomb was found on the historic site.
A member of the public handed the mystery object to a member of staff at the ticket collection hut last Thursday.
A quick internet search aroused concerns and, as the object looked like it had been in the sea and had been moved already, the decision was made to move it away from the public and into the office in the museum.
Holy Island Coastguard and police were then called and they ordered the site to be evacuated.
Bomb disposal experts were asked to attend and Berwick’s all-weather lifeboat brought them, along with police officers, from the mainland because the causeway was inaccessible.
With help from coastguard officers, they sealed off an area in a field behind the priory and blew up the item, thought to be a live anti-personnel mine.
Lynn Rylance, area manager for English Heritage in the North East and Cumbria, said: “We can confirm that a World War One landmine was handed in to a member of staff at the priory last week. Police were notified and a specialist bomb disposal unit was called in. The bomb was detonated in a controlled environment and the priory given the all clear.”