On 1-5, 7 miles South of Chula Vista. San Ysidro, the world’s busiest border crossing, is not a pretty sight: a constant flurry of cars, buses and people crossing the United States – Mexican border. Within walking distance on the Mexican side, the city of Tijuana makes an interesting day out. Packed with Californians on shopping sorties, however, Tijuana is hardly typical of Mexico. There are no formalities when you cross from the U.S. but returning non-U.S. and non-Canadian citizens face the usual border checks.