Start from the right place, and you can just walk to Latin America. The place is the end of the tram line in San Diego, California's second city, from this year linked to Gatwick by air. In less than half an hour, a tram rattles through the indulgences of suburban southern Californian life, then deposits you at the front line between First World and First, rich and poor, north and south,

The busiest border in the world acts as a valve. Going south, you are borne along in a shuffling tide of humanity from the tram terminus across a tagliatelle of footbridges and through a macaroni of concrete corridors, and swept south of the border.

Immediately, you must make several exchanges. Dollars for pesos; order for chaos, but a gentle brand of anarchy that somehow restores a dimension that has vanished north of the border; and swap your preconceptions for reality. Not a single citizen slumbers beneath a sombrero; no moustachioed bandidos here. Tijuana is a big, fast city whose main industry is catering to the repressed needs of US citizens. Whether you need dentistry or drugs, you can get it more cheaply and easily in the Estados Unidos de Mexico than the United States of America.

And this is where the problems begin. The US authorities take great interest in people and their possessions heading north. Expect long queues and close questioning. I first went to Mexico with my Scottish grandmother. On the way back, she was apprehended because of a visa discrepancy. Only after hours of questioning at an office beside the humid, fume-choked highway, were she and I were let back in to California. On reflection, I'm not sure it would have been that bad if we'd had to stay. SC