The building that now houses the Museu Náutico in Vila was originally Ilhabela's jail and courthouse — the Antiga Cadeia e Fórum — a squat colonial structure whose iron-barred windows and heavy masonry recall the island's role as a Portuguese administrative outpost in the 18th century. Ilhabela's colonial authorities built fortifications and defences along the western channel during the 17th and 18th centuries to protect against pirate raids, and the old civic buildings that survive in the Vila quarter are among the best evidence of that period still visible above ground.
The Nautical Museum inside focuses on the island's maritime heritage, which is substantial: Ilhabela's waters have claimed over 30 ships, and artefacts from several of those wrecks are on display alongside historical maps, navigational instruments, and records of the island's caiçara fishing communities. It's a small museum but gives useful context to anyone planning to dive the wrecks or explore the coast. Admission is inexpensive and the visit pairs well with a circuit of the Vila quarter, including the adjacent Igreja Matriz Nossa Senhora D'Ajuda e Bom Sucesso across the square.