GETTING THERE: Visitors can fly to the Toluca, Morelia or Mexico City airports and then rent a car or hop a bus to the town of Angangueo or the city of Zitacuaro, both of which offer lodging and transportation, usually buses or taxis, to the butterfly reserve. It takes about three hours to get to Angangueo by car from Toluca or Morelia and about four hours to get there from Mexico City. People unfamiliar with the area should hire a car or take a tour bus for the 30-minute trip from Angangueo to the El Rosario sanctuary as the roads can be twisty and sometimes dangerous. In late November, Continental Airlines had roundtrip tickets on February flights from Chicago O'Hare International Airport to Toluca for under $500.

ANGANGUEO: Tourism office in Angangueo, Mexico, is at 011-52-715-156-0044, but you may not be able to get information in English. Hotels include El Hotel Albergue Don Bruno (011-52-715-156-0026, rates begin at $80) or Las Margaritas (011-52-715-156-0149, rates begin at $27). They can arrange transportation to the Monarch Butterfly Biosphere Reserve. Transportation is also available from the town's main plaza.

FOOD: Bringing food into the reserve is prohibited, so plan on staying for a few hours and then heading back down to the entrance to enjoy quesadillas or tostadas at stands that cluster there.

WHAT TO WEAR: Because weather can be extremely cold in the morning, dress in warm, layered clothing that can be easily shed, and wear comfortable hiking boots. A raincoat might also be a good idea, since mist and light rains are common.

WHEN TO GO: The butterflies begin arriving in November and leave by late March. The best time to see them is between 10:30 a.m. and 1 p.m., when they are at their most active.

TIP: On cloudy days, the butterflies remain still to preserve body heat. It's advisable to plan your trip to include an overnight stay in the area so you can come back on a different day if the weather doesn't cooperate.

OTHER ATTRACTIONS: Morelia is a beautiful, colonial city with great food and arts and crafts; Patzcuaro, a tiny village on a breathtaking lake, has a great food and crafts market and two lovely plazas and is known for its Day of the Dead celebration in early November; Tlalpujahua is a tiny, picturesque town, an ideal place to stop for lunch.

ECOTOURS DE MEXICO: or 011-52-322-222-6606.