Austria has a park that submerges underwater during summer, turns into lake

The 'Grüner See' or 'Green Lake' is a park located in Austria which submerges underwater from late spring through early summer. The park's lake, which only spans 21,500 square feet during late summer, autumn and winter, widens to cover almost double the area when the ice melts. Submerging the park benches and pathways, the lake can run 40 feet deep.