Moving between different D&D universes

I have a group of mid-high level players. As part of some D&D shenanigans, I wanted to have them plop into Athas (Dark Sun) as a surprise joke. But knowing them, sadistic as they are, they might want to return.

How would it be possible for them to move between universes or return to their home universe? I know I can just DM it any way I want, but I wanted to ask you all if that’s possible on their behalf. For instance, a would using a wish spell, a gate, or the Plane Shift work (using game mechanics)?

Would Athas be considered a plane?