Musée sous-marin du Pays de Lorient

Housed inside a massive WWII submarine bunker — now carrying a 20th-century heritage label — this museum dives deep into the Battle of the Atlantic and the claustrophobic reality of life aboard a submarine. You can explore a real French torpedo boat that patrolled these waters from 1960 to 1989, now docked right on the harbor quays. It's a genuinely gripping visit, and one of the most impressive things to do in Lorient.