Yellow River Forest, see http://www.iowadnr.gov/forestry/yellowriver.html
The area overall is remarkable.
Algific slopes in several areas, with unusual flora. Thus year-round ice caves. Karst topography. If no longer considered strictly 'driftless,' nonetheless not so much glacially sculpted as the rest of the state.
Nearby Effigy Mounds National Monument--fine bear mounds and a bird mound, among others.
Not so good for climbing except when the ice is in here and there in the area.
Beautiful timber and fine views, with what for Iowa are very substantial elevation changes.
Very good fishing on the Mississippi, and some native trout streams.