Beirut, Lebanon - Most people passing by the busy Adlieh intersection in east Beirut are probably unaware that several floors underground, hundreds of people languish in a makeshift detention centre. "It's like a tomb," Abbas, a former detainee of the underground facility, told Al Jazeera.

Although it is intended as a temporary holding centre for foreign nationals, some inmates have been held at the facility for weeks, months or even years. Once used as an underground parking lot, before being converted to a prison in 2000, former inmates have reported being held in inhumane conditions, with no natural sunlight, minimal ventilation and frequent overcrowding.