EXCLUSIVE: “Ask yourself: ‘Can you live in a bathroom for 10 years?'” Welcome to Red Onion State Prison. Built on an Appalachian mountaintop nearly 300 miles from any urban center, it’s one of the 40-plus Supermax prisons that dot the United States. Let’s just say it’s not a place you’d want to visit — let alone be incarcerated.

Here’s a clip from Solitary, Kristi Jacobson’s documentary that offers an unprecedented look inside one of the facilities that journalists call “black zones.” Members of the press normally aren’t allowed within Supermax walls, and the few who are usually are stripped of recording equipment. Jacobson secured unrestricted access to Red Onion over the course of a year for Solitary, which is from HBO Documentary Films and will premiere Saturday at the Tribeca Film Festival. It features telling interviews with the inmates about their violent childhoods and the dangers of prison life. We also hear from the corrections officers, who often struggle to maintain their humanity.

The film will air on HBO in September. For just a moment, think about sitting alone until then in a tiny room — then multiply that time frame by 25 or more. Scared straight?