Arenal Hanging Bridges, Costa Rica - A three kilometer hike through the Costa Rican rain forest. There are six suspension bridges, with the largest one at just under 100 meters long and 45 meters off the ground.
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. This is amazing!