The colonial city of Guanajuato has everything—art, architecture, mummies—except Americans.

Five hundred years ago, Cortés's armies descended on what are now Mexico's heartland states of Guanajuato, Querétaro and Michoacán, drawn by the promise of gold. Today it's the resulting cache of small, perfectly preserved colonial cities lying within easy reach of one another that makes this undervisited region irresistible. The most famous town around here, without a doubt, is San Miguel de Allende; but a mere 50 miles away as the crow flies (though a thousand miles away in terms of attitude) lies a small city that, for my money, beats that arty-gringo haven hands down: Guanajuato, eponymous capital of the state, birthplace of the painter Diego Rivera and once, in its silver-mining days, among the richest cities in Mexico. I'm not knocking San Miguel—it's stunning, it has some lovely hotels, and you can get blueberry waffles and veggie burgers—but I am here to praise its charming neighbor to the west.

Guanajuato looks like it's been poured into place, its pastel-painted colonial villas, basilicas and churches dripping down either side of a steep, narrow ravine and arranged along crooked cobblestone callejones (alleys) that suddenly climb 17th-century stone steps or flare out into tree-shaded plazas. The city manages to be simultaneously peaceful and bustling. Its students outnumber its tourists, and the paseo—the evening stroll—is taken very seriously. Instead of a zócalo, or town square, Guanajuato has the Jardín de la Unión, a red-tiled, café-lined triangle with a topiary roof of Indian laurels and a well-used bandstand. The university is often said to be the best in Mexico, but not for its bulky, pseudo-Moorish mid-'50s architecture—it's one of the more boring buildings in town. At the other extreme are the churches (like the Jesuit Templo de la Compañía, with its fizzy ultra-Baroque facade); Teatro Juárez, a neoclassical theater full of decadent velvets, gilt and chandeliers, opened by the then all-powerful general Porfirio D’az himself in 1903; and the forbidding Alhóndiga de Granaditas, a granary-turned-prison, site of one of the first battles of the War of Independence and now a rather good museum.

This city has been under UNESCO World Heritage protection just since 1988, yet its beauty is not only unchanged, it's barely even besmirched by traffic—thanks to an ingenious network of underground roads, created in the '60s from an old riverbed. It's thrilling to twist and hurtle through these tunnels by taxi, getting voyeuristic flashes of somebody's washing overhead, then land suddenly in a sunlit central street.

I needed the taxis because I was staying at Guanajuato's best hotel, Quinta Las Acacias, which stands in the posh parkland neighborhood of Presa de la Olla, outside the city center and up the ravine. Built in the 19th century as a patrician summer retreat, Las Acacias still has the air of a slightly eccentric manor house, with decor split fifty-fifty between colonial Victorian and mod Mexican. I prefer the peaceful rear rooms in the latter style, especially the spacious topmost suite, next to a secret walled garden, with its vista of rooftops visible from a circular Jacuzzi. The hotel is one of 30 Mexico Boutique Hotels, a new collection of small, privately owned deluxe hotels (think Mexican Relais & Châteaux), which I found invaluable in devising my mini colonial town tour.

Sadly, La Casona del Cielo, widely held to be the city's number one restaurant, was closed during my stay, so I had no opportunity to try its pasta in cuitlacoche sauce or salmon with coriander and Jamaica flowers. But it was no hardship foraging among the small, unpretentious local places for freshly mixed guacamole and fajitas in just-pressed tortillas and snacking at bakeries and the fragrant, cavernous Mercado Hidalgo. Since the heartland is extremely fertile, the market is exemplary—especially rich in strawberries and nopales (cactus leaves) but also abundant with mangoes, guavas, peaches, guanabanas and just about every other fruit you can imagine. The city is also sugared with gaudy dulcerías, stalls and shops bearing stacks and stacks of cellophane-wrapped sweetmeats, from primary-colored taffies and jellies to the delectable cajeta, the goat's-milk caramel that's a specialty of the nearby village of Celaya.

But if Guanajuato's dining is undistinguished, its museums are unique. Along with Museo Casa Diego Rivera, which houses dozens of the painter's early works in his childhood home, the city harbors two peculiar museums I wouldn't have missed for the world. The Museo Iconográfico del Quijote is a beautifully restored colonial villa stuffed with artistic renderings of the Ingenious Knight of La Mancha, ranging from the unbelievably beyond-kitsch to works by Picasso and Dalí. (During the city's October Cervantes Festival, this place really comes into its own.) Then there's the Museo de las Momias, which attracts hordes of visitors every day to its gruesome display of a hundred-odd twisted, leathery, naturally mummified corpses disinterred from the local cemetery. A salacious tour guide weaves byzantine fictions (in Spanish) around these nightmarish figures, illustrating the cheerful Mexican death obsession better than any Day of the Dead fiesta. On second thought, the momias are the only thing in Guanajuato I wouldn't have minded missing.