How big is the gap?
You could fit bookcase strip to the walls and side of the wardrobe. The wardrobe needs to be moved for access. Mark the heights across the gap before you move the wardrobe as the floor could be uneven.
An alternative, if it fitted, would be something like a small "Gnedby" bookcase on each side? https://www.ikea.com/gb/en/p/gnedby-shelving-unit-white-40277143/
You could place one behind another, leaving the back off the front one , making it deeper. Or further back and add long shelves between them for depth.
You might find the gap too small and it would be more useful shifting the wardrobe to one side, having a bigger gap to fill.
Another way would be to carefully drill through the inside of the wardrobe outwards, so that you either screw into the side of a shelf, ( not strong) or into a bit of timber (2x2) that you've already screwed onto the shelf underside
Another way would be to carefully drill through the inside of the wardrobe outwards, so that you either screw into the side of a shelf, ( not strong) or into a bit of timber (2x2) that you've already screwed onto the shelf underside
Hmm, drilling through is an interesting idea. Maybe there is a way to securely fix something on the other side.
Don't think it would be the prettiest, just thinking of more storage space.
If you get some contiboard cut down in width, then cut in lengths that will fit the depth of the wardrobe, you have shelves that will fit. Buying contiboard that's edged on both ends which is at least halved saves doing it yourself.
Then possibly fit a bit of 2x2 under the edge, allowing it to be screwed into, or find some angle brackets that could support the shelves. By taping or even hot glue gunning a nut to the holes of the L bracket, you should be able to drill through the inside of the wardrobe with enough precision that allows a bolt to go through and find the nut.
Measurement would be key
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