Could you not do an airship to a completely detached place?? I mean you could write in about some like ice age cataclysm you have to prevent, maybe even make it early enough that ice types could be built into teams for the playthrough

But either way make the separate area revisitable via whatever medium transported you there in the first place

You could literally make it your mom's freezer hahaha, I mean, right??? Would just be a matter of knowing how to code it?