Many people wonder, "How does Crossroads work?" Well, my theory is based on Einstein's theory of relativity, as it was presented to me in a much simplified version. Okay, here goes:
Einstein's Theory of Relativity (simply put):
Okay, here's how it works: Time and Space are relative. When you think, "This class is taking years!" to you it is. To others, it may be taking half a minute. The way time passes is relative, so even though we measure it, that measurement is, in a sense, an average of how time passes. Got it so far? Okay.
As for space, there are an infinite amount of possible realities. Einstein's idea was something like this:

The red line represents a barrier between us and the infinite realities. The world as we know it is in one of those dips. To see the other realities, we have to get up on one of the humps. Then we'd see them all.
Here's where my Crossroads theory comes in.
When you open/find a portal to Crossroads, you are going through a portal, through a portal on the "hump," and to Crossroads.

The green circle would be the portal you opened, the pale purple circle is the one on top of the "hump," and Crossroads is the gray circle. The journey described above is represented in orange, and would take slightly less than .0134 seconds.
So to sum it all up:

The big, black circle is Crossroads. The little gray circles represent the journey from our D/W/U to the "hump," and the green lines are the journey from "hump" to Crossroads.
Ta-da! And that's how I think Crossroads works. . . wait, isn't "Crossroads works" an oxymoron?
Okay, that's how it functions. Thanks to Crossroads personnel, it "works." Ever.