The exchange has two endpoints
The offset-passage room demonstrates crossing a divider by exchanging with a crystal. Both the Wizard and the object move: a swap that advances the character may send a useful crystal back into a narrow opening. The object need not be on the immediately adjacent square.
Use the room to determine the target
Walls, other objects and the approach direction determine which exchange is available. The crystal-bank room shows how swaps pass through a crowded layout. Mixed-hero routes can use a teammate as a swap partner; that does not make every occupied square a safe destination.