HONG KONG — Among the crowds on Kweilin Street in the run-down Hong Kong neighborhood of Sham Shui Po, Alla Lau darted between street signs, peering at the backs of them until she found what she was looking for. She beckoned a group of tourists, mostly white, in flip-flops and with American accents.

“There,” Ms. Lau said, pointing to a handwritten white sticker in Chinese characters that referred to the grimy building across the street. It was an advertisement for one of Hong Kong’s notorious cage apartments, where, for as little as 1,200 Hong Kong dollars a month (about $154), people could rent a cage to sleep in, stacked three deep, with barely space to sit up.

The group Ms. Lau led had signed up for a tour of the less glamorous underbelly of this fabulously wealthy city. Over the course of three hours, tourists learned about Hong Kong’s underpaid foreign domestic workers, its freewheeling street vendors and the suicides afflicting young students pressured by their parents to succeed in school.

Despite the horrid conditions in the cage apartments, Ms. Lau said, they still were not cheap. Per square foot, the monthly rent was more than that of the costlier apartments in Hong Kong, one of the world’s most expensive housing markets, and many people living in the cages make far less than the city’s monthly median income, roughly 12,000 Hong Kong dollars a month, or about $1,540.