The world of Grimm Therapy is divided into three parts:

1. The Really Real World of school and classes and parents and teachers and bullies. This is the place where magic of Make Believe mostly just gets you in trouble. Your Special Friends are very reluctant about showing their face around here.
2. Make Believe isn't so much a place as a state of mind -- you can do make-believe anywhere, and with anyone else who understands 'how to play'. Your special friends usually want you to be in Make Believe all the time, because they can do more there and have more fun. Sometimes, if you're really good at Make Believe, echoes of your heroic stories even echo over to the Other Side.
3. The Other Side -- some kids call it the Twilight Kingdom, some kids call it neverneverland, but whatever the name, the thing everyone agrees on it is that it's the place where Make Believe is Real and the Really Real World isn't real anymore. This is the place your Special Friends came from, and the place they say you can get to if your Make Believe is Really Really Good.
   It's also a really dangerous place.

How to Get from One Part of the World to Another

Starting Make Believe Here, our young sorcerer starts out in the Really Real World and isn't very happy about it. It's clear that he has things to do and places to be. By using his imagination (i.e.: Lore vs. [Resistance -- default to 5 dice], with bonuses for time spent), the Sorcerer is able to make the place where he is into something much more suitable for his kind of Make Believe. This is a fairly simple thing to do when one is alone, which can be made either easier or more difficult when a Sorcerer is working with another Sorcerer (or just a bunch of other 'normal' kids), depending on whether or not participants have different ideas about what the Make Believe should be about. (Appropriate group Sorcery rules (cf. p. 90) apply.)

Growing Your Make Believe The level to which an area is fully pulled into Make Believe really only depends on how far the young sorcerer is willing to take it. Time = Effort. Again, having additional kids along to play with makes a Make Believe much stronger, __provided__ everyone can agree on the basic final result (contested Will rolls are quite useful here for getting people in line, and come Covers or Pasts might assist). For all intents and purposes, playing Make Believe is a series of rites (Call it Contact with repeat attempts possible (even after successful rolls) but without the Humanity Checks), led by at least one 'Kid Sorcerer'.

Opening the Other Side Once the Make Believe power reaches a certain level (defining that level is really your call -- bonus dice from the previous Make Believe (Contact) rolls will assist here), it's a fairly simple thing to move entirely over to the Other Side. (Use the Summoning rules versus a variable default Resistance. There's no inherent Humanity check, though your own actions while leaving for the Other Side might require one anyway.) Note that this is not usually done unless really necessary, since many misadventures can result. Your Special Friend (Demon) will always do whatever they can to help you make these rolls successfully. Always.

Moving through the Other Side Although this Sorcerer is obviously powerful enough to fully command the obedience (if not loyalty) of the creatures he encounters in his journey, young Sorcerers should be cautioned: the Other Side is DANGEROUS, and should be approached with CAUTION.

Getting Back Once a Sorcerer finishes his quest on the Other Side (or simply becomes bored), the process of returning back to the Really Real World is essentially the same process as getting there in the first place: you just have to retrace your steps (with all the inherent risks that might entail) and 'finish the story', which might not be a simple thing at all. If back-tracking is a problem, returning to the Really Real World via some other point of access is possible, although that solution carries its own set of problems (and potential parental complications).

Picking a Good Spot As a general rule, there are areas in the Really Real World that are more or less conducive to Make Believe -- some places have a kind of 'background count' that results in bonus dice for certain kinds of Make Believe occurring in that area. The downside to this is that playing Make Believes of a different kind in that area is usually opposed by those same dice.

Going it Alone The overall difficulty of getting to Make Believe is not prohibitive. Really, anyone can manage it, at least in their own little bubble of quasi-reality, but it can be an empty experience when the only person one has to play with is oneself.

Playing with Friends When you manage to pull others into your Make Believe (either other Sorcerers or simply Mundane Children willing to get into your idea for a game), your Make Believe will be more enjoyable and more powerful (bonus dice rolling into not only your Make Believe rolls, but into efforts you make inside the Make Believe that flow along the lines of the current 'story'). Involving others might also have other beneficial effects (opening a largely unimaginative child to the wonders of Make Believe could even be worth a Humanity Gain roll), but might also be potentially dangerous for those involved who are otherwise ignorant of this kind of Magic: more powerful Make Believes will echo into the Other Side, carrying with it the names and pseudo-identities of those who participated right to the hairy ears of those you'd rather not deal with.

Note:

Having read this, you are now obliged to go buy a copy of Where the Wild Things Area. Go on, git. :)