Lots of great skiing mountains also double as hiking trails in the warmer months. However this area in Austria has got to be the only place this doubles as a hiking spot and a great place to scuba dive.
Located at the foot of the Hochschwab Mountains, in Tragoess, Styria, Green Lake is one of the most bizarre natural phenomena in the world. During the cold winter months, this place is almost completely dry, and used as a country park where hikers love to come and spend some time away from urban chaos. But as soon as temperatures rise, the snow and ice covering the mountaintops begin to melt, and the water pours down, filling the basin below with crystal-clear water.
That first picture would be great for an "explain this picture" contest. :)
Grüner See, 8612, Bruck an der Mur, Styria, Austria