If you don't have a designed-in niche but do have a big walk-in shower, contemplate hanging floating shelves to the shower wall, like this roomy bathroom from Louis Duncan-He Designs. Snagged a sizable-scale storage cabinet (reward points if It is really vintage) although not particularly guaranteed where to put it? https://flenzy.store/white-3-tier-over-the-toilet-metal-storage-rack/