The Old Customs House Museum is a small local-history stop on Baltrum, set in a former customs building. It helps explain the island's seafaring, tourism and everyday life, which can otherwise be easy to miss amid beach walks and Wadden Sea excursions.
Do not expect a large museum; the appeal is scale and context. It works best on a slow island day, especially if weather interrupts beach plans or you want to understand more of Baltrum than dunes and ferry timetables.