The Wadden Sea is the reason Büsum is more than a beach town. At low tide the North Sea retreats into a huge, wet plain of sand and mud, part of the UNESCO-listed Wadden Sea system shared by Denmark, Germany, and the Netherlands. It looks empty at first, then turns busy: worms, shells, birds, channels, and the marks left by water that will return fast.
Do not wander far out alone unless you know the tide tables and local conditions. Guided mudflat walks are the best way to understand the place, and they are safer. Bring shoes that can get filthy, a windproof layer, and a willingness to adjust your plans around the tide.