Ruins reach across centuries to fire the imagination and fuel travel plans. The very best make you feel young, small, and utterly amazed by the architectural chops of the ancients. Among the many amazing ruins that still exist today, a few stand out as the trip of a lifetime.

No matter which ruins you visit, a few rules hold true: Time your trip for the less crowded times of day, often early or late. Give yourself plenty of time, as some ruins require days of exploration. Hire a knowledgeable guide, since the history is rich but the signage is often cursory. And get beyond the most popular parts of the ruin; you'll need a bit of quiet space to appreciate this kind of ancient majesty.

Here they are: