If you want cooler weather and a laid back atmosphere, head up the the Keweenaw Peninsula in the UP. The entire peninsula is surrounded by Lake Superior so if you are near the water it is very comfortable in the hot part of summer. Plus the lake temp is usually in the 50s so a quick dip will cool you off ;).
Check out Ontanagon, Hougton, Hancock, Calumet and Copper Harbor. All are great little towns.
I would recommend the Porcupine Mountains State Park (right on the lake), McClain State Park (also on the water) and Fort Wilkins State Park.
If you have never been I would highly suggest seeing Lake Superior either from MI or MN or heck, head up into Ontario. There is nothing else like it in the world.
There is also some beautiful places in Northern MN. The area around Voyagers National Park is very nice too.