Earlier quoted context omitted.
I suspect the reason that it’s done indoors is that, most places with a high enough density of humans for this practice to be available, the outside is a dangerous place for a tripping patient. Someone driving by blasting a rap album out their window could send a trip in some bad directions.
Also, it’s a clinical study. They need to control the conditions or it’s not science.
Just adjacent to her office was a "trip room", probably constructed when the building was build in the 70s (?). It was round, completely lined with acid orange fabric, upholstered like a pasha's tent and filled with cushions in every colour imaginable. No doubt it had a superlative quadraphonic sound system installed. It also had a large, smoked glass window, for "observers." Not ideal for mushrooms perhaps but for other things...