We wanted to use the 23 cm we had between our shower wall and our washing machine and dryer for something useful. We needed a solution for storing our laundry so we decided to do our very own hack.
We bought two METOD Base Cabinets as they were just 20 cm wide and thus slim enough to fit in the room available yet making it possible to enter the shower.
We put the cabinets on top of each other and fastened them with screws. As these cabinets are supposed to be used with a table top we mounted one of the shelves in the top to close the cabinets from above.