Alternate Ending
If you free the Sorcerer that Darkhunter wishes you to take to the Red Tower near the start of the game you will gain access to three areas you normally wouldn't near the end of the game along with a new ending.

Embark on an inspiring mission of human connection beyond the UCA. Sam — with companions by his side — sets out on a new journey to save humanity from extinction. Join them as they traverse a world beset by otherworldly enemies, obstacles and a haunting question: should we have connected?