Barcelona’s popular Sant Sebastià beach was partially evacuated after an unexploded bomb was spotted in the water nearby.
Explosive experts moved the bomb out to sea, where it was successfully detonated, police said, in an operation involving the Spanish navy.
The device was thought to date from the 1936-39 Spanish Civil War and contained about 70kg (154lb) of TNT.
A police officer found the bomb on Sunday 80ft (25m) from the shore.
Parts of Sant Sebastià beach, which draws millions of tourists every year, remained closed to the public on Monday.
The beach, together with Barceloneta, is one of the most famous in the capital of Spain’s independent-minded Catalonia region.