Founded in 1548, Guanajuato was one of the first strongholds of Spanish culture in Mexico. Today, it's a beautiful colonial-style state capital and university town. Revenue from silver mining financed its superb architecture, which has a distinct Spanish flavor.
Guanajuato is an absolute must-see. The city is a feast of color and architectural style: medieval, Gothic, neoclassical and colonial. Winding streets, covered bridges, arches and alleys beckon alluringly. You can spend weeks exploring this city, at every turn coming across some fascinating building, church or museum. UNESCO has classified it as a World Heritage Site.
Museums in the town include the birthplace of Diego Rivera (it displays works by him and Frida Kahlo, as well as excellent temporary exhibits), the Museo del Pueblo and the Museo Iconografico Don Quixote (everything you ever wanted to know about Miguel Cervantes and his famous character). Also worth some time is the Alhondiga de Granaditas, a massive grain-storage facility that is now a state-funded history museum. However, by far the most popular attraction is the Museo de las Momias, a creepy exhibition of exhumed corpses preserved by Guanajuato's unique soil conditions.
The center of town is at the bottom of a steep canyon, so the streets are winding and best explored on foot. Be sure to see Callejon del Beso (Street of the Kiss), which is so narrow that two people can kiss by leaning out the windows of facing buildings. Vehicles are prohibited from the center and instead move through the Subterraneo, an underground street that replaced an old sewer system.
The Cervantes Festival, held the first three weeks in October, features dance, theater, opera and musical groups from all over the world (accommodations should be reserved far in advance). 220 mi/350 km northwest of Mexico City.