Spend nine days migrating with native monarch butterflies—the best time to witness their flight is January. Head west to Parque Nacional Eduardo Ruiz in the city of Uruapan ("Eternal Spring") named for its lush vegetation—and venture to surrounding colonial villages, such as Angahuan, on low-impact foot trails. The highlight of the trip is the climb to El Rosario, a thriving butterfly sanctuary where millions of the delicate creatures inhabit a 10,000-foot-high protected forest. Great Adventure People (G.A.P), in partnership with the sanctuary, has planted hundreds of trees so that the butterflies can migrate safely.

Trip Tip: On your free day in Mexico City, ask your hotel to arrange a visit to the ancient pyramids at Teotihuacán, 30 miles northeast, and, en route, the Basilica of Guadalupe.

Luxury Level: Although the hotels are simple, most are family-run and located in colorful colonial houses from the 1800's.

G.A.P Adventures; 800/708-7761; gapadventures.com; $795 per person, meals not included; January 5-14 and 19-28, February 2-11 and 16-25, March 1-10.