El Paso International

Beneath the Guadalupe Mountains of southeastern New Mexico lies one of the great cave systems on Earth — over 119 known caves, dissolved out of an ancient reef not by water but by sulfuric acid rising from oil and gas deposits below, a rare process that left enormous chambers. The Big Room is almost 4,000 feet long and one of the largest underground chambers in North America; you descend 750 feet, by trail through the natural entrance or by elevator, into a decorated wonderland of stalactites and stalagmites. And every evening from spring to fall, the other spectacle: hundreds of thousands of Mexican free-tailed bats spiral up out of the cave mouth at dusk in a roaring column to hunt — a ranger program runs at the amphitheater for the bat flight.

Trinity Site — the precise spot where the world's first atomic bomb detonated on July 16, 1945, at 5:29:45 AM Mountain War Time. The Gadget plutonium implosion device, identical to Fat Man, vaporized its 100-foot test tower in a yield of about 21 kilotons. The crater of fused green glass (trinitite) is still mildly radioactive 80 years later. The site sits inside the closed White Sands Missile Range about 60 nm south of KABQ; it's open to the public ONLY twice a year — first Saturdays of April and October — by Army-led tour. The white gypsum dunes of White Sands National Park are 30 miles southwest, and from the air the contrast between the snow-white dunes, lava flows, and the Tularosa Basin is unmistakable. Restricted airspace (R-5107) covers most of the range.

In July 1947, a rancher found strange debris on a ranch near Roswell, and the Army Air Field briefly announced it had recovered a "flying disc" — then quickly corrected to a weather balloon. Decades later the incident exploded into the most famous UFO story in the world, fueled by claims of recovered alien bodies and government cover-up (the debris is now generally attributed to Project Mogul, a secret balloon program to detect Soviet nuclear tests). Roswell embraced it completely: the International UFO Museum downtown, an annual UFO Festival, and streetlights shaped like alien heads. Beyond the kitsch, Roswell is a real ranching and dairy town on the Pecos River, gateway to the surprising Bottomless Lakes (NM's first state park) just east.

McDonald Observatory sits atop Mount Locke (6,790ft) and Mount Fowlkes (6,660ft) in the Davis Mountains of West Texas — the highest mountain range in the state. The site was selected in 1932 for its dry air, stable atmosphere, and exceptionally dark skies, among the darkest in the continental United States. The Otto Struve Reflector (82-inch), dedicated in 1939, was the second-largest telescope in the world at the time. It is joined now by the Harlan J. Smith Telescope (1968) and the 9.2m Hobby-Eberly Telescope (1999), one of the largest optical instruments ever built. Weeks after Apollo 11 landed, McDonald astronomers bounced a laser pulse off the corner-cube reflector Buzz Aldrin had placed on the Sea of Tranquility — a billion photons sent, a single photon returned — and measured the Earth-Moon distance to within inches. The observatory still runs lunar laser ranging today.