Wilson Lake, KS
With 9,000 acres of water surface and 100 miles of picturesque shoreline, the man-made (by the US Army Corps of Engineers) Wilson Lake comes out of nowhere to shock you with its beauty and red-rock outcroppings. You can fish, water ski, play sand volleyball, or mountain bike. And yes, this is Kansas.
The one most-do thing: Appreciate the surrounding nature from the best vantage point... on the water, in a kayak