The Forgotten Worlds mod for The Witcher 3: Wild Hunt is a mod that allows you to revisit the locations in The Witcher 3: Wild Hunt that you can't reach outside of the quests that took you there in the first place. So if you're wondering what's this mod about, remember the Isle of Mists? Remember the alien worlds when you followed Avallac'h through the portals in "Through Time And Space" quest? If you don't remember any of what I just mentioned, then maybe you shouldn't use this mod as you may not have advanced far enough in your quest and this might spoil upcoming parts of the game. But if you do remember, have you ever wanted to return to those places? Well, that's pretty much what this mod is about, to allow you to revisit the only places in The Witcher 3 that you can't reach outside of the quests that took you there in the first place.