Imagine this with a canvas pad or marrow yoga lounger thingie across the top under your former window. Then the towels and oils/salts for the tub could be stored inside it. Made simply with bamboo butcherblock.
Most Unusual Writing Room! Sometimes the best ideas come while you're taking a relaxing bubble bath. Sudden stroke of inspiration? Don't let that disrupt your bath time, just turn the tub into a writing desk and you're good to go!