Somewhere in the world, you can find a river that looks like it's bleeding. It's a place so intensely red that early visitors there believed they'd discovered a passage that led straight to the underworld.

The water in this place, known as "red river," wasn't tinted by clay or seasonal algae blooms. The river has an acidity level that rivals battery acid. Fish can't survive in it, plants won't grow along its banks and the water is so toxic it would burn your skin on contact. Yet this crimson waterway has been flowing for over 5,000 years, carving its scarlet path through an otherwise green landscape.

The river gets its otherworldly appearance from an extraordinary concentration of dissolved metals, including iron, copper, zinc and silver. The water is so saturated with minerals that it's essentially liquid ore, with a pH level around 2. Walking along its banks feels like visiting an alien planet, which is exactly why NASA scientists come there to study it.

Can you guess where this strange red river flows?

Although many of the creatures one would expect to live near or in rivers are absent, life has still found a way to survive in the red river. Extremophile bacteria and other microorganisms thrive in the harsh conditions, creating ecosystems that scientists believe might be similar to what could exist on Mars. The river has become a natural laboratory for astrobiology, helping researchers understand how life might persist in the most unlikely places.

The crimson color isn't natural. Instead, it's the result of thousands of years of mining activity that has leached metals from the surrounding hills into the water system. Phoenicians, Romans and countless civilizations since have extracted precious metals from the area around the river, gradually transforming what was once normal into a spectacular but polluted waterway.

OK, have you made your guess?

This is Rio Tinto in southwestern Spain, whose name literally means "Red River." Flowing for 100 kilometers from the Sierra Morena mountains to the Gulf of Cádiz, it passes through some of the world's oldest mining regions and has become an unlikely destination for both tourists and scientists.

Would you visit this liquid fire? Tell us in the comments!