Green Fitness Studio, 232 Varet Street, is tucked into an unassuming block populated by industrial manufacturers and artist lofts. Once you climb the stairs, what lies in front of you is a windowed exercise room split between weights and cardio equipment. If you keep walking straight through the facility, past the locker rooms, you’ll find yourself standing on a wood-paneled floor in what first clocks in as a vast auditorium hall. Further on, positioned at the far reaches of the floor is a boxing ring, and before that two dozen stationary bikes.