Accelerated breathing, loud evocative music and optional bodywork, in pairs, over several hours. Grof built it explicitly as a non-drug route to the states he had been studying with LSD before it was scheduled, which makes it the most direct substitute on this page rather than a lateral one.
Participants work in pairs and swap roles. One breathes, lying down with eyes closed, for two to three hours while the music carries a deliberate arc from driving to quiet. The other sits, keeps them safe, fetches water, and does not interpret anything. Afterwards you draw a mandala and the group sits together to talk.
The experiences reported span the full range that psychedelic research describes, including perinatal and transpersonal material, which is the specific territory Grof's model was built to account for. Intensity varies enormously between people and between sessions.
The name matters commercially. Holotropic Breathwork and Grof Breathwork are trained credentials with an actual certification body behind them. A great deal of what is sold as breathwork retreat is a weekend of fast breathing run by someone with a 200-hour certificate, and the difference is not visible from a website.
A representative shape drawn from how these are typically run. Use it as something to ask against, not as any one centre's timetable.