MICHAEL CRONIN's job as a college admissions officer took him to India two or three times a year, so he had already seen the usual sites - temples, monuments, markets - when one day he happened across a flier advertising "slum tours."

"It just resonated with me immediately," said Mr. Cronin, who was staying at a posh Taj Hotel in Mumbai where, he noted, a bottle of Champagne cost the equivalent of two years' salary for many Indians. "But I didn't know what to expect."

Soon, Mr. Cronin, 41, found himself skirting open sewers and ducking to avoid exposed electrical wires as he toured the sprawling Dharavi slum, home to more than a million. He joined a cricket game and saw the small-scale industry, from embroidery to tannery, that quietly thrives in the slum. "Nothing is considered garbage there," he said. "Everything is used again."

Mr. Cronin was briefly shaken when a man, "obviously drunk," rifled through his pockets, but the two-and-a-half-hour tour changed his image of India. "Everybody in the slum wants to work, and everybody wants to make themselves better," he said.

Slum tourism, or "poorism," as some call it, is catching on. From the favelas of Rio de Janeiro to the townships of Johannesburg to the garbage dumps of Mexico, tourists are forsaking, at least for a while, beaches and museums for crowded, dirty - and in many ways surprising - slums. When a British man named Chris Way founded Reality Tours and Travel in Mumbai two years ago, he could barely muster enough customers for one tour a day. Now, he's running two or three a day and recently expanded to rural areas.