The town's quirkiest sight lurks across the bay from the main promenade. The concrete opening in the harbour wall is the mouth of a natural underwater cave that the Soviets turned into a secret nuclear submarine factory officially known as Facility-825. Today you can breach the huge nuclear-blast-proof doors and wander through parts of the facility, which features repair docks, mess rooms and, thankfully, an arsenal that is now empty. You can take a one-hour Russian-language walking tour or a ½-hour boat tour, leaving on the hour and at 4.45pm. Take a jumper; it gets chilly inside.
