Lava Tube Cave From another pinner: One of the most exciting things to do at the Lava Beds is to visit lava tube caves. Though many are hidden in the wilderness, some caves have ladders and trails, and vary from easy walks to strenuous excursions. Temperate and moist year round, caves are often very different from the outside world, forming “micro-climates” full of fascinating life such as bats, ferns, and sparkling bacteria. Lava Beds National Monument, California, USA
Nemo 33, Brussels, Belgium. The world's deepest swimming pool. The pool has two large flat-bottomed areas at depth levels of 5m (16 ft) and 10m (32 ft), and a large circular pit descending to a depth of 33m (108 ft). It is filled with 2,500,000 litres of non-chlorinated, highly filtered spring water maintained at 30°C (86°F). The complex was designed by Belgian diving expert John Beernaerts as a multi-purpose diving instruction, recreational, and film production facility, and opened in 2004.