See the Río Tinto in Spain
The Río Tinto appears first as an improbable stripe through the earth: water the colour of rust, mineral banks in red and ochre, and the remains of railways and mines beside it. The landscape looks otherworldly because its chemistry and human history are inseparable. A responsible visit uses established viewpoints, museums or the heritage railway around Minas de Riotinto and Nerva. The colour comes from acidic, metal-rich water shaped by natural geology and thousands of years of mining, so this is a place to understand rather than a wild swimming spot. Check current opening times and transport between the dispersed sites, reserve timed elements where required and allow several hours. Stay on authorised routes, keep out of active or unstable workings, avoid touching or entering the water and do not collect rocks or industrial remains. Count it complete when you have seen the river from a legitimate public location and learned how its geology and mining story produced this landscape. Add it if a river that links ancient industry, extreme-life research and startling colour makes you want to look closer.