Ten days of silence, no reading, no writing, no phone, roughly ten hours of sitting a day. The best-known network runs entirely on donation, so cost is genuinely not the barrier. It is also the hardest thing on this page, and people underestimate it because it sounds passive.
The format most people mean is the Goenka-lineage ten-day course: same timetable at every centre worldwide, same recorded discourses, no charge at all for first-time students, funded only by donations from people who have already sat one. You give up your phone and your books at the door and you get them back on day ten.
The insight (vipassana) centres in the Western lay tradition run a wider programme: weekend introductions through to three-month courses, teachers who are available for individual interviews, and a sliding-scale fee plus dana to the teacher. They are gentler on arrival and considerably more expensive.
What actually happens is not mystical and not marketed as such. Attention gets narrow, then unstable, then occasionally very quiet. Days four through six are where most people want to leave. The reported effects that overlap with psychedelic experience tend to arrive late, unbidden, and without a facilitator managing them for you.
A representative shape drawn from how these are typically run. Use it as something to ask against, not as any one centre's timetable.