The Gaomei Wetlands are about an hour west of central Taichung, on the coast where the Dajia River meets the Taiwan Strait. At low tide, an enormous mudflat is exposed, with crabs, mudskippers, and seabirds. A long wooden boardwalk runs out into the mud and is the standard way to walk in without sinking.
Sunset is the magic hour and the standard time to visit, but it is also when the crowds are heaviest. Get there at least an hour before for the best light. Combine with a quick stop at the Qingshui railway station and the Tatung Distillery on the way back.