Blue Lake Cave (Brazil)
Mato Grosso do Sul region in Brazil (and especially the quiet town of Bonito) boasts many marvelous underground lakes: Gruta do Lago Azul, Gruta do Mimoso, Aquário Natural. The world famous "Gruta do Lago Azul” (Blue Lake Cave) is a natural monument whose interior is formed by stalactites, stalagmites and a huge and wonderful blue lake. The beauty of the lake is something impressive. The Blue Lake Cave has a big variety of geological formation but impresses mainly for the deep blue colored water of its inside lake.
Hell Gate (Turkmenistan)
Called by locals The Door to Hell, this place in Turkmenistan is situated near the small town of Darvaz. When geologists were drilling for gas, 35 years ago, they suddenly found an underground cavern that was so big, all the drilling site with all the equipment and camps got deep deep under the ground. None dared to go down there because the cavern was filled with gas, so they ignited it so that no poisonous gas could come out of the hole, and since then, it has been burning. Nobody knows how many tons of excellent gas has been burned for all those years but it just seems to be infinite.
Wave Rock (Australia)
The Wave Rock is a natural rock formation located in western Australia. It derives its name from the fact that it is shaped like a tall breaking ocean wave. The total outcrop covers several hectares; the "wave" part of the rock is about 15 meters high and approximately 110 meters long. One aspect of Wave Rock rarely shown on photographs is the retaining wall about halfway up the rock. This follows the contours and allows rainwater to be collected in a dam. It was constructed in 1951 by the Public Works Department, and such walls are common on many similar rocks in the wheatbelt.