Foregoing any sort of chronological order, today we'll have a look at the very first world you'll see as a player. When you load the module, you're greeted by a cutscene which looks like that:
No, I won't tell you how long it took me to create it.
And then you met Melvin, the annoying wizard who sends you running after the sphere.
At the beginning, that's all you'll see of this dimension. Later, if you have advanced enough in the main quest or if you trigger one of two unrelated quests, you'll get access to the rest
of the island.
It's a very small island, and there isn't much to do there.
Besides Melvin, there are two other characters you can talk to.
But the island isn't supposed to work as a dimension to explore. In fact it's your QG, the one place you will come back to often while you explore the rest of the Multiverse. Melvin can sometimes provide a solution to the problems you face out there, and besides, you're safe here... as safe as it gets next to a wizard with inscrutable intentions, anyway.