Teide looks like Mars but smells much better,” says my Spanish friend Rocio as I mention my upcoming trip to the UNESCO World Heritage site, a sprawling national park in Tenerife, Canary Islands, a Spanish archipelago off the coast of northwestern Africa. Rocio waits for the confused look to cross my face, then explains with a grin: The atmosphere on Mars contains stinky sulphur. So if humans could breathe on Mars (which we can’t since there is barely any oxygen in the atmosphere), it would reek of rotten eggs or a sewer that’s been backed up for days. The vague olfactory description doesn’t prepare me for the sight that awaits.

