The squat stone bulk of Lamu Fort dominates the centre of the old town, just a couple of streets back from the seafront. It is early 19th-century, built by Omani craftsmen with thick coral-rag walls, deep window slits, and a central courtyard that catches the breeze. From the upper ramparts you look out across the rooftops to the harbour.
Today it houses the Environmental Museum (small collection on the Lamu archipelago's ecology) and is also the venue for the National Museums of Kenya's library and conference space. It is cheap to enter and the rooftop view is worth a half-hour on its own.