I recall an old PC game, which I'm pretty sure came from the 90's. I also don't think it was available on consoles, so that might narrow it down for you. I played this game for about an hour at a friend's house and never did get my hands on it, so the details are pretty vague.
What I do remember is it had a 3rd person view, was somewhat of an adventure game (Non RPG), and had something to do with elemental worlds/bosses. It also had a hub for these worlds, which is what I remember the most.
The hub was kinda bowl shaped, but not a true bowl. Let me explain. When you appear in this hub you're standing on a grassy path and need to walk the curved path "down" to the center of the hub. You can't walk around the "edge" of the "bowl" because it doesn't exist, off to the sides of you is nothing but air. When you walk down the path and hit the center of the "hub" at your immediate left begins the display of the different worlds and they continue around your front and end off to your right. I believe there are 5 different worlds. I remember one of the worlds was an "earth" (as in dirt) world, one was ice (or water), and I think there was even a shadow (or air) one. Each world type was represented in this hub as a castle or gateway of some kind. I also believe when you defeated a world you gained the power of that world, but can't be sure of that.
I really wish I had more detail for you, but that's pretty much all I can recall. Couldn't tell you how "main stream" this game was. It wasn't something as popular as Starcraft, but it wasn't a "dollar bin" special either.