This event is hosted in Trackmania and in the title(s) Trackmania² MultiEnvi. You can participate on your own and registration is not required.
The 90MC (90 Minute Contest) is a track building competition. The challenge is to build an entire map in only 90 minutes. Each edition has a unique theme which is introduced at the start of the contest each time it is held. The contest is hosted by Mania Exchange.
The contest is listed here as MultiEnvironment, but you're allowed to build in individual environments: Canyon, Stadium, Valley, Lagoon.
For more information about the contest, visit the main topic on MX.
For each edition, a new topic is posted in the Competitions Forum at the start of the contest.