Set on a hillside above Mirror Lake near Reedsburg, Wisconsin, the Seth Peterson Cottage is a small Usonian house designed by Frank Lloyd Wright with Thomas Casey supervising and ranks among Wright’s last designs. Commissioned after Seth Peterson lost an earlier cottage in a 1958 fire, it was begun in 1959, but Peterson died in 1960 before completion. Compact and carefully planned around a masonry core, it combines sandstone, glass, flagstone floors, radiant heat, and a central fireplace. Completed by Lilian T. Pritchard’s family, it later deteriorated in state park use before preservationists restored it. Reopened in 1992, it survives as a preserved Wright building and rentable retreat.