place i'll go: Austria's Green Lake in the Hochschwab Mountains is a hiking trail in the winter. The snow melts in early summer and creates a completely clear lake. The lake has a grassy bottom, complete with underwater trails, park benches, and bridges.
Split Rock Lighthouse, Minnesota (by Rikk Flohr) North shore of Lake Superior near Beaver Bay. Completed in it has remained dark since 1969 except for once a year on November to commemorate sailors lost in Great Lakes shipwrecks