The Polhem dry dock, completed in 1724, is the oldest functioning dry dock in the world and one of the most remarkable pieces of engineering in Sweden. It was designed by Christopher Polhem, the Swedish Archimedes, and built into the granite bedrock of the dockyard island. The dock is large enough to hold a ship of the line, and its original sluice mechanism — a wooden gate system that could drain the dock in hours — survives almost unchanged.
As part of the naval dockyard that is a UNESCO World Heritage Site, the dock can be visited from Marinmuseum on Stumholmen. Standing beside it, you get a tangible sense of the scale of 18th-century Swedish naval ambition — this was built to maintain the largest warships afloat, and the workmanship is extraordinary. The granite walls show the tool marks of the men who cut them by hand over several years.