2) Rio Tinto, Spain
Meandering through Southern Spain, Rio Tinto (also called the Rio Tinto Blood River) is home to expansive opencast mines that give it its surreal, lunar-like landscape. Its growth has devoured not only mountains and valleys but even entire villages, leading to the relocation of its residents to specially-built towns nearby. Named after the reddish streaks that give it its color, Rio Tinto is brimming with ferric iron, sulphates, and protons. Its microbial biodiversity is attributable for its high acidity (pH 1.7 to 2.5) and has gained a lot of scientific interest as of late. The extreme conditions in the Rio Tinto river may be similar to other locations within our solar system, such as subterranean Mars. Photo credit.