Le Redoutable

This is the world's only publicly accessible former nuclear submarine capable of carrying ballistic missiles — and you can walk through it at Cherbourg's Cité de la Mer museum. Le Redoutable racked up an impressive 20-year service history: 51 patrols, 70 days each, covering 1.27 million kilometres beneath the surface. It's a genuinely rare thing — cold war hardware you can actually step inside and explore.