The Kaai (also written De Kaai) is the smock mill standing on Sloten's south rampart, built in 1755 as a corn mill and restored to working order in the 20th century. The miller still grinds wheat and rye on Saturdays during summer, and the milled flour is sold from a small shop beside the wheel.
Visitors can climb the narrow internal staircase up to the cap when the sails are turning, and the views across the polder from the upper deck are the best in town. Open Saturdays from April to October; admission is a few euros.