The world's largest tidal flat system disappears underwater twice a day

Stretching along the coasts of the Netherlands, Germany, and Denmark, the Wadden Sea is a vast expanse of sand and mud flats that's fully exposed at low tide and submerged again at high tide. It supports millions of migratory birds each year and is one of the last major intertidal ecosystems on Earth still functioning at this scale.

— Wikipedia contributors, Wadden Sea — UNESCO World Heritage Site, listed 2009