Mexico City/Santa Fe
Santa Fe is in the northwestern area of Mexico City. It is the newest and most modern part of the city, as almost all of it has been developed only in the past twenty years; this puts this district in stark contrast with Mexico City's other districts, especially the Centro Historico. Many multinational and Mexican companies alike are headquartered here, with multi-million-dollar towers that scrape the sky.
Santa Fe was developed in the early 1990's on the remnants of an old landfill -- yes, a junk yard turned into a modern business district. The first institution to settle here was the Universidad Iberoamericana, a high-end institution for the local wealthy that saw its building collapse in the 1985 earthquake. It wasn't until the early 2000's that Santa Fe gained attention as a well-developed business district, radically different from the rest of the city, because of its ultramodern architecture and contrasting wealth lifestyle signs.
The paranoia that the local authorities have against photographers in Mexico City goes double for Santa Fe. Guards will yell "no photo" at you, or even shoo you away from a building if you as so much approach with a camera, tripod or no.
Santa Fe is not served by the Metro, so the only ways into the area are by car, taxi or bus. Cars and taxis are probably the fastest, but are certainly not the cheapest. However, Santa Fe is served by Mexico City's RTP network and very frequently by pesero buses, which leave from Tacubaya station (Metro Lines 1, 7 and 9) and take around 30-45 minutes to get there. Look for buses that say "Sta. Fe" in the window.
You will recognize instantly when you are in Santa Fe, when the two-lane road widens to lessen stop-and-go traffic and grand office buildings replace stucco shanties. If you're on the bus, it will travel around the skyscrapers rather than go inbetween them; a good place to get off and look around is when the bus is on Avenida Vasco de Quiroga, or on the opposite end of the line of skyscrapers. Don't wait too long though, because the bus continues onward into the residential area of the hills.
If you just want to see a radically different side of Mexico City, Santa Fe is the place to be, with lots of skyscrapers and modern architecture. Also, take a stroll in the Alameda, the central park of Santa Fe.
There's not much to do; Santa Fe is a business district first and foremost, so during nights and weekends it looks like a ghost town.