These subterranean models show Mexico City's central square during three different eras.

A giant hilltop cross marks the location of a sanctuary with stunning views of Acapulco.

Roman ruins, natural methane fires and a lovely beach.

Roman ruins top white travertine terraces formed by ancient hot springs.

A deadly ancient portal to the underworld.

Seven early Christians were sealed into a cave where legend has it they slept unharmed for centuries.

Ancient serpentine sacrifice holder that has stood the test of time.

This remarkably well-preserved Egyptian plinth is pretty well traveled for a giant piece of stone.

A marvel of Byzantine engineering under the streets of Istanbul.

Legend says if you stick your thumb in the hole and it gets wet your wish will be granted.

Five sultans and their families rest in eternal splendor, teeming with overlooked beauty and drama.

1513 Turkish world map, full of European state secrets and snarky commentary.

A section of the long chain that blocked enemy ships from entering Constantinople.

This column celebrates Rome's victory over the Goths, and may be the oldest Roman monument in Istanbul.

The legendary luxury train passage is commemorated with a charming museum inside its former eastern terminus.

Thousands of rusting train cars have been slowly falling apart on the edge of Greece's second largest city.

This striking sculpture of Icarus honors Greece's fallen flyers.

This ancient Greek place of assembly and marketplace is being revealed layer by layer below the modern Athens cityscape.

An ancient octagonal weather station named for the eight Greek gods of wind.

Where commuters walk through remnants of an ancient Greek necropolis.

The only surviving choragic monument is a trophy awarded in 334 BC for the winning dramatic chorus.

The Cycladic architecture makes this Athens neighborhood feel like an island paradise hidden in the shadow of the Acropolis.

Heralded as the world's first theater, these ruins are often overlooked as they reside in the shadows of the Acropolis.

Large collection from the 3rd millennium BCE.