Forgotten realms is just one "region" in the setting. It is one universe in a multiverse of regions. This multiverse is called Planescape. All d&d games that I know about utilize that setting. In Planescape any arch way or opening can be a potential portal to another realm. You just need the right key. The key could be an object, a leaf, or a childhood memory or a song that can take you to another world when you walk through the archway of which there are an infinite amount. The forgotten realms is one of these places. But I'm repeating myself. You played torment so you know this as it takes place in the city of sigil the city that lies at the nexus of the multiverse.
I mean there are books dedicated to just describing the d&d setting and if they gave out awards for settings, these books would win. The novels aren't part of this. That's what I'm saying.