Near Jakarta's historic port are several 17th-century VOC (Vereenigde Oost-Indische Compagnie; the Dutch East India Company) warehouses that comprise the Museum Bahari. This is a good place to learn about the city’s maritime history, with a sprawling series of galleries covering everything from nautical legends and famous explorers to WWII history in the archipelago. Also included in the price is the 1839 Syahbandar Menara observation tower, just before the entrance to the maritime museum.
In Museum Bahari you'll find a sextant (used for astronomical navigation), various traditional boats from around Indonesia, the shell of a giant clam, plenty of pickled fish and a lighthouse lamp or two. The sentry posts outside are part of the old city wall.