La Villa de Guadalupe is in the northern part of Mexico City, part of the delegación (borough) of Gustavo A. Madero. It is home to the Basílica de Guadalupe complex (known often simply as "La Villa"), which includes Tepeyac Hill. The complex is perhaps Roman Catholicism's holiest site in Latin America.
Founded in 1563 as La Villa de Guadalupe, the area houses the shrine of Our Lady of Guadalupe. It is at the foot of the Tepeyac Hill, where many believe that the Virgin appeared to St. Juan Diego (canonized by John Paul II in 2002, making him the world's first indigenous American saint). The Old Basilica, which dates from 1709 (construction began in 1531), began sinking due to weakening foundations and unstable ground in the 20th century; it was replaced by the New Basilica in 1976. The Old Basilica has since been restored and has now re-opened; both places celebrate Mass, often concurrently. Pilgrims from around the world flock to this space to pay homage to Our Lady of Guadalupe; framed above the altar of the New Basilica hangs the tilma (apron) of Juan Diego, upon which the Virgin's image was imprinted.
Metro Line 6 (red) has a stop (La Villa-Basílica) about 2 or 3 blocks from the basilica complex. Line 6, a fairly isolated line which runs east-west to the north of the city, has several connections ("correspondencias") to lines that service the rest of the city: Line 7 (orange) at El Rosario, Line 5 (yellow) at Instituto del Petróleo, Line 3 (green) at Deportivo 18 de Marzo, and Line 4 (teal/aqua) at Martín Carrera. From any of these stations, hop on Line 6 to La Villa-Basílica. Exit the station, follow the crowd through the narrow market-like sidewalk full of food stalls, and onto the Calzada de Guadalupe (the main thoroughfare). From here, the Old Basilica should be visible; simply follow the crowd the couple blocks to the gates of the basilica complex. The New Basilica will be on your left, and straight ahead, the Old Basilica and the Capilla de las Capuchinas.
You can also take a taxi from anywhere in the city if you'd rather deal with Mexico City's eternal traffic than the Metro.
Street food. Plenty of it to be had, especially in the corridor that leads from the Metro stop to the Calzada de Guadalupe.
If you are less adventurous, there is a McDonald's on the Calzada de Guadalupe just before the gates of the complex.
La Villa de Guadalupe is worth the commute. Stay in other, safer districts, such as Polanco or the Zona Rosa.