Only a small amount of preparation will be necessary for this visit. Early Day 90, everyone will be given a circular badge by the Ringmaster, who will tell you that you'll need to wear it if you plan on travelling to the new touring location. Where you wear it isn't important as long as it's accessible.
Later on Day 90, the Nightrunners will be sent out to do a quick security check of the new location - so, they'll be discovering all of this sooner than anyone else, and it will be their jobs to report on it. There are a few security concerns, which will be outlined OOCly for them in the comments below. As well as whatever can be gleaned from this general info post.
Entrance to the new location will be done with the transition portal through the woods, out through a "forested" area filled with weirdly low polygon trees. Glamours will be in effect, though the appearances of the locals are variable enough that appearances will not have to significantly change in a lot of cases.
Mainframe is a city inside of a computer. No, not like the Matrix - as opposed to a virtual reality simulation that the denizens think is real life, it really is a civilization of programs that know what they are and live accordingly. In contrast, the local's perception of any world outside of the Net is very hazy, and "the User" (IE, the beings that actually use the computers they live in) is seen as either a god-like entity or malevolent demon, depending on who you ask. Either way, the User is most often something the inhabitants of the Net are forced to combat rather than cooperate with. Life within the Net is the only world they know, and the Ringmaster will advise that you leave it that way, or else they'll probably get all weird about it.
The Net is actually a real, physical plane of existence for those inside of it, so visitors from the carnival will be under the same threat of injury or death that they would be otherwise. The programs have very different biological features (or a lack thereof), of course, but the glamours will be able to conceal these differences as long as no one does anything really weird like bleeding all over the place. This also means that you'll be able to take objects back into the carnival as souvenir, and that they won't just poof into metaphysical data when you leave. Weird, though.
This isn't the exact Mainframe as in the show, to be clear. There is a different Guardian and different viruses at play, for those familiar. Aesthetically and culturally, however, it is very familiar - though about three times the population size. Ostensibly they are without those 90's animation budgets.
( MORE PLOT DETAILS BELOW )