Scientists who search for life on Mars and beyond test their ideas in a handful of extreme places on Earth. Five of them are open to travellers. So is America's UFO trail, where the stories are bigger than the evidence.
One of the driest places on Earth, with soil chemistry close to Mars. NASA has tested life-detection drills here, including its Atacama Rover Astrobiology Drilling Studies project.
Visiting: San Pedro de Atacama is the base for desert trips, and the region's clear skies make it a stargazing centre too. Combine it with the Paranal Observatory on our Space on Earth page.
Yellow, green and orange pools so acidic, salty and hot that a 2019 study in Nature Ecology & Evolution found no active life in them. It showed that liquid water alone does not make a place habitable.
Visiting: only on organised tours, usually from Mekele. The Afar region has had security problems, so check your government's travel advice before you book.
A blood-red, acidic river whose microbes live on iron and sulphur. From 2003, NASA and Spain's Centro de Astrobiología drilled here to practise searching for life below the surface of Mars.
Visiting: the river runs past Minas de Riotinto in Huelva province, where the mining park runs a historic tourist train along its banks. An easy addition to our Spain guide.
A hole about a mile wide and 570 feet deep, blasted out roughly 50,000 years ago. Apollo astronauts trained here because it looked like the Moon.
Visiting: just off Interstate 40 between Flagstaff and Winslow, with a museum on the rim. In 2026, guided hikes down the Astronaut Trail to the crater floor opened to the public for the first time.
What remains of an asteroid strike about two billion years ago, one of the largest impact structures on Earth. It became a UNESCO World Heritage Site in 2005.
Visiting: the river town of Parys, south-west of Johannesburg, is the base for guided geology tours, hiking and rafting. See our South Africa guide.
No physical evidence of alien visitors has ever been made public. Two places in the American Southwest built their identity around the idea anyway, and both are fun to visit if you know the real story.
The town that became famous for a "flying saucer" in 1947. It has a UFO museum and research centre, alien-themed streets and a UFO festival every summer, usually around the start of July.
State Route 375, named the Extraterrestrial Highway in 1996, runs about 98 miles past the edge of the restricted Area 51 base. Rachel, a town of about 50 people, has the alien-themed Little A'Le'Inn motel and diner.
In July 1947 the Roswell Army Air Field announced it had recovered a "flying disc" from a nearby ranch. Decades later, books and witness stories claimed a crashed spacecraft, alien bodies and a government cover-up. Many people still believe them.
The military said within a day that it was a weather balloon. In 1994 the US Air Force said the debris came from Project Mogul, a secret balloon programme to detect Soviet nuclear tests. A 1997 report said the "bodies" were most likely memories of crash-test dummies and other 1950s incidents.
Area 51 itself is closed. It is an active, guarded US Air Force site. Stay on the public road and obey the warning signs at the boundary.
See where scientists are looking for life right now, or visit the radio telescope where the modern search began, SETI at Green Bank.
Sources: NASA Astrobiology (Atacama), ScienceAlert (Dallol study), NASA Astrobiology (Río Tinto), NPR (Meteor Crater, July 2026), Vredefort impact structure, Nevada State Route 375 and Britannica (Roswell), checked 14 October 2026.