The Croatian Maritime Museum is located in the Gripe fortress above the eastern end of the Riva, a solid 17th-century stronghold with a view over the harbour and the islands beyond. The collection covers Croatian maritime history from the early medieval period to the 20th century, with particular emphasis on the 18th and 19th centuries when Dalmatian sailing ships were a significant force in Mediterranean trade.
The Gripe fortress itself is worth the visit for the architecture and the view — the walk up from the harbour takes about 15 minutes and the panorama from the ramparts takes in the full arc of Split harbour, the Riva below, and the islands stretching south. The museum is often overlooked in favour of the palace-area attractions, which means it's rarely crowded. Opening hours can be unreliable; check ahead before making a special trip.