What is the importance of Mexico City in the novel, The Eagle’s Gift?

After recuperating in Veracruz, the apprentices go to Mexico City, where they spend two days as tourists before author Carlos Castaneda takes them to an airline office into which Don Juan Matus had once pushed him, causing Carlos to slip through the crack between worlds. Carlos then takes them to the place in Alameda Park where he and Don Juan had talked about that experience. At this point, Carlos has no idea how to control the apprentices as a group.