The single most distinctive thing you can do on Juist is to walk on the sea floor. At low tide the Wadden Sea — the long band of intertidal mudflats between the island and the mainland — drains to expose a vast flat of grey-brown silt, criss-crossed by channels, dotted with mussel beds, and crawling with lugworms, cockles, and crabs.
Guided walks ("Wattwanderungen") set out from the southern shore of Juist during the two hours either side of low water. The standard tour is a two- or three-hour loop along the edge of the flats — you do not walk to the mainland from Juist, the channel between is too deep — and a guide explains what is living under your feet. Wear short trousers and old shoes you do not mind getting muddy. Solo expeditions onto the flats are dangerous and forbidden.