Meditation camps (Hindi: sadhana shivir) have been a feature of the sannyas landscape since 1964. Prior to that, Osho was lecturing, traveling and becoming well known as a riveting speaker, but he saw that people were not being transformed, so he introduced camps, extended retreats where the focus was experiential rather than filling one's head with concepts. At these retreats, he spoke, often at length, but the event was not over when he stopped speaking. Then it was time to visit the interior landscape, to experiment with his techniques and use his words as signposts of things to look for, guidance regarding pitfalls and so on. Most of the day(s) would be spent in self-exploration, using a variety of ways to ask "Who am I?" Deeper and deeper.
From the back cover of The Perfect Way, an English translation of his discourses at the first camp in 1964: "These discourses are the outcome of Shree Rajneesh's first testing of a new idea, the meditation camp, envisaging an intensive programme lasting several days, which enabled the seekers to dive totally into an atmosphere of meditation."
As they evolved, camps were held several times a year in various formats, lasting a couple of days to as many as fourteen, and in "exotic" locations mainly around the northwestern states of India: seaside resorts, hill stations, usually but not always away from cities. Nargol, Matheran, Mt Abu and others became fabled places in the sannyas iconography.
Traveling to such places came to an end in 1974 after Osho moved to Pune, but the camps did not end. At Shree Rajneesh Ashram, it became possible to have these intensive retreats more often. As the camps evolved in Pune, meditations were first led personally by Osho and then by others who had imbibed them sufficiently to be able to lead them. But even with others nominally leading the meditations, Osho still came out to talk daily.
And the camps took on a more standardized format, which ran more or less the same for the last five years of Pune One, and that was: 6-7 am, Dynamic; 8-9:30ish, Discourse; followed by Sufi Dancing, Vipassana, Nadabrahma and Kundalini and then an evening meditation which would be Gourishankar for one camp and Nataraj for the next. The camps ran for ten days, from the 11th to the 20th of each month.
The easy availability of such opportunities to jump fully into Osho's meditation techniques made it easy for newcomers to get a feel for it, though they weren't only for newcomers. Camps continue to this day in one form or other around the planet, for one day, for weekends, for 21-day Dynamics or Mystic Roses and so on.
A timeline of Osho's historic meditation camps given before the move to Pune can be found at Talk:Osho Discourses. with details of when and where, books associated and more.