This is not a climbing route, it is only used for descent. You will follow it if climbing Kilimanjaro on the Machame, Shira, Lemosho or Umbwe route.
As restricted as all of this sounds, there are possible variations. Some of the routes have alternate paths for some sections, you can combine different sections of different routes, and treks can be extended to include a night in the crater itself. (Only recommended to very experienced and well acclimatized climbers. This camp is extremely high.)
Theoretically you could also walk right around the base of Kibo.