De Rat is a working wind-powered sawmill on the edge of IJlst, and the most compelling reason to visit the town. It is one of the last sawmills in the Netherlands still powered by wind, and on days when the sails are turning you can watch the whole process — logs arriving by water, sawn into planks by a large reciprocating blade driven directly from the mill shaft.
The interior is open for guided visits. The wooden machinery is enormous and loud when running, and the guides explain the mechanics clearly. Allow about an hour. Admission is modest; check seasonal hours before visiting as the mill does not run every day.