It seems everything is about the multiverse these days right? I am not really sure when I first got hooked on the idea of other universes. In tabletop, I was always aware of the other planes of existence in D&D. I never ran adventures in them, but it was nice knowing they were there. It gave a dark and expanded view to the worlds we played in. I sadly missed out on Planescape, so I never got to explore the City of Doors and the planes they led to. In fiction, I would say the one inspiration that stuck with me was Hellraiser. The idea of this dark realm that could be touched by ours through a puzzle box just resonated with my mind. An alternate plane that was a dark labyrinth is directly reflected in the plane where Kaldrath was imprisoned in my fiction. I always related the other world as dreamlike and insubstantial. This grew as I read fictions based on the lands of the fae, where elfland was described as timeless and strange. I would also say the strange world of the Dark Crystal also influenced me with the idea of the convergence. Except, instead of two being becoming one, I saw two universes colliding.
All of this created the basis for the lands of Atheles and the Navirim, two universes linked and colliding. Later came the idea of the In-Between, as Dane and I needed a place for the fey and elves to go during the Disappearance. And before I knew it, this became one of the main themes in my gaming world and writing. Taking this backdrop of crashing worlds, I then get to ask, what would your character do in the Dark Return?