One of Venezuela's hottest venues for musicians and sports stars was, for part of the last decade, a maximum-security prison run by its own inmates.

"Party at the PGV tonight," local DJs would announce over the radio. Visitors would come from the nearby towns, or all the way from the capital, Caracas, 100 miles away.

Their rigid, if convoluted, code of conduct was maintained by gangs and an arsenal of heavy weapons. Infractions were met with brutal punishments.

Visitors were considered sacred, and off-limits.

Outside/Inside

From the outside, there were vestiges of ordinary prison infrastructure: High fences heavily crowned with barbed wire, control towers, and checkpoints manned by military officers armed with rifles and machine guns.

But look closer, and you would have seen a thin fence. On the other side, manning the PGV's entrance, a select group of prisoners held far more powerful guns, and many more of them.

La Rutina

For inmates, life at the PGV was like walking a tightrope over a pool of sharks.

Abiding by an unwritten code was obligatory, and prisoners lived under the constant threat of ruthless punishment if they stepped outside of it.

Documentary photographer Oscar B. Castillo had extraordinary access to Venezuela's PGV prison during an extended period when it was controlled by inmates. You can view the full photo essay on insider.com