An extensive collection of fine art devoted to man's best friend.

The oldest volcanology research center in the world.

Erotic art covers the walls of the largest ancient pleasure palace.

2300-year-old Roman road connecting the empire.

This historic recreationist school churns out warriors that may very well have had a fighting chance in Rome's pits of the day.

Hidden beneath the famous St. Peter's Basilica is a veritable city of the dead that may hold the remains of St. Peter himself.

The underground sanctuary of a mysterious ancient cult.

The engineering wonder and pleasure dome of a much-maligned emperor still holds undiscovered secrets.

One of several skulls claiming to belong to the beheaded St. John the Baptist is on display at this Roman church.

This former Roman Catholic Church still contains the embalmed hearts and organs of 22 popes.

Architectural monsters are devouring this palace's every door and window.

Museum dedicated to literary greats of the Romantic Period is also the home in which Keats met his untimely end.

The only visible reminders of an elaborate engineering project that kept the tower from reaching the tipping point.

A lover's walk between hilltop towns, decorated with graffiti love notes.

The quirky gift from West Berlin for the 1968 World's Fair still stands in Hemisfair Park.

These boots are made for selfies.

The 40-foot-tall votive candle is the largest of its kind.

Three hundred years of preserved Spanish colonial history in San Antonio.

Jesus' footprints and the first catacombs in the world.

Walk 2,300 feet above the ground on the "Troll's Tongue."

This gracefully curving formation looks like a massive wave that was suddenly turned to stone.

"Looks so real, it's scary!"

A stunning silver lining to global warming's gloomy cloud.

Stay overnight in the world's most sleekly designed rabbit hole, free of charge.