The bare, dusty ground is littered with rusty blades and crack pipes. The area reeks of urine and garbage.

At least three times a day, Charly Roué is drawn to this neighborhood, one of the most sordid in Paris, always following the same ritual .

After panhandling tens of euros at cafes not far from some of the most popular tourist spots, he heads to the northern edge of the city, where he can buy crack cocaine at La Colline, or the Hill, France’s largest open-air market for crack .

Many of the drug users who come here day after day “compare La Colline to hell,” said Mr. Roué, 27, who has been using drugs on and off since he was 14. “The locals who live nearby and suffer from the chaos we bring must call it hell too.”