Eight kilometres south-west of the city centre, on the headland at Møvik above the Skagerrak, sits the heaviest piece of artillery ever installed on Norwegian soil — a 38 cm Krupp naval gun built into a vast concrete bunker as part of Hitler's Atlantic Wall in 1941-43. The bunker, the gun, the ammunition store, the underground crew quarters and the surrounding battery positions have all survived almost intact, and form one of the most complete surviving German coastal defence installations in Europe.
The museum is small but extraordinary. You go inside the bunker, up to the breech of the gun, through the magazine. There are guided tours every couple of hours in summer; outside the season the gun is still visible from the headland. Allow ninety minutes; bring a jumper for the bunker, which stays cold even in August.