My “cellar storage area”, as it was described by the estate agent, or “damp cave”, as it’s described by me.
A couple of years back, I decided to stop paying for a nice, clean dry storage unit and spend a few months’ worth of the rent on a bunch of waterproof storage boxes (and some big silica gel packs, because I figured “waterproof” doesn’t actually mean “can be stored indefinitely in a damp cave and remain dry inside”.)
So far it’s working out pretty well. I keep a list of what’s in each of the boxes — labeled “A” to “N” in bright silver Sharpie — in OneNote, so I can go straight to whichever box I need when I want something, which averages about once a month. Everything seems pretty well-preserved, even the “nostalgia” box, which is mostly old papers and photos.