It’s a mystery why the Sinagua people abandoned Montezuma Castle—preserved pre-Colombian dwellings in Camp Verde, Arizona—in about AD 1425. The best theories suggest drought or conflicts with other Native people and newcomers. What is clear is that they left behind a 20-chamber castle cut into a limestone cliff. Montezuma is one of several Sinagua archeological sites in the American Southwest: see them on a single tour or stop by en route to Sedona or the Grand Canyon.

The Ajanta and Ellora Caves are UNESCO World Heritage sites about 60 miles (100 kilometers) apart in Maharashtra, a state in central India. They’re among the largest cave temple complexes of their kind in the world, with some carved from massive single blocks of stone. Ajanta holds nearly 30 2nd-century Buddhist cave temples; Ellora’s 34 caves are newer and more varied, built for Hindu, Jain, and Buddhist worship. You’ll need one day for each complex and can also see the Mini Taj Mahal nearby.

Nearly 900 monumental carved human figures called “moai” dot the landscape of Easter Island, a remote volcanic island in the southern Pacific. The island is a World Heritage Site, much of it protected within Rapa Nui National Park. Built by the Rapa Nui people, the moai resemble upright humans with big heads, and are thought to assist in ancestor worship. Reaching the island is challenging—limited flights from Santiago are your best bet—but once there it’s easy to explore multiple moai sites.

Nicknamed the “Rose City” for its pink sandstone cliffs, Petra is a 2-millennia-old archeological city set within a narrow canyon in southwest Jordan. The much-photographed Al Khazaneh temple has a recognizable 150-foot-tall (45-meter) Greek-style facade. A UNESCO World Heritage Site and one of the New Seven Wonders of The World, the archeological site comprises tombs, temples, and Roman structures famous for their rock-cut architecture—think of it as a lost city surrounded by magical mountains.

One of the New Seven Wonders of the World and a designated World Heritage Site, Chichen Itza is among the greatest Maya archeological sites in Yucatan. The sprawling site occupies 4 square miles (10 square kilometers) east of Valladolid with temples, ball courts, and a cenote (freshwater sinkhole). The massive central step pyramid, called the Temple of Kukulcan or El Castillo, dominates the ancient city, which has around 26 official archaeological sites.

About one-sixth of Italy’s UNESCO-listed sites are in Campania, a hefty proportion for one of Italy’s 20 regions. Surrounded by ruins in Herculaneum and Paestum, Pompeii is the most impressive: the sprawling archeological site is a nearly intact town, famous for being miraculously preserved under volcanic ash from the eruption of Mt. Vesuvius nearly 2,000 years ago. Here, you can walk Roman cobblestone roads; behold millennia-old frescoes and mosaics up close; and explore ancient temples.

Another UNESCO World Heritage Site, Great Zimbabwe was a medieval-era city in the southeastern hills of Zimbabwe near modern-day Masvingo. The ruins favor curves over straight lines and are built in a freestanding style without mortar—an impressive feat of engineering for the time. They're also among the largest stone structures south of the Sahara Desert. Visitors can tour ruins with an acropolis, a large circular wall, high towers, and mud-brick houses where villagers once lived.

Machu Picchu is an Incan citadel perched nearly 8,000 feet (2,440 meters) above the Urubamba River Valley in the Andes Mountains. A hugely popular backpacking destination via the Inca Trail or alternative routes, the ruins appear as if by magic, with ancient plazas, terraced hills, and astronomically-aligned structures amid a tropical mountain forest. Like all good ruins, Machu Picchu cradles lasting mysteries, including who built the sophisticated lost city and exactly how.