Suomenlinna comprised of a few godforsakened rocky islands about 10km from Helsinki. It was well-fortified by the Swedes, as you can see.

With many cannons, all at the ready.

But although the walls were literally 10 feet thick, they were no match for the Russians. They besieged the fortress for two months before the Swedes surrendered.

These days, the islands are besieged daily by tourists, and the inter-city ferries from Helsinki to Tailinn and Stockholm.