RICHMOND, Va. — Three times a week, Robbie Norris, a lean, 50-year-old yoga teacher, hops into his blue 1992 Volvo station wagon with his yoga mat and heads to his class in a drab brick building.

He barely glances at the barbed wire as he strides through the metal detector. He exchanges his driver’s license for a visitor’s pass, navigates a labyrinth of hallways, security guards and the buzzing and clanking of gates, and makes his way to a windowless room.

A dozen women, scarred, tattooed and in blue and yellow jumpsuits, are waiting, splayed on donated yoga mats under harsh halogen lights.