I'm furnishing a new room in an apartment. When my landlord remodeled this apartment, he created a nook in the wall, 20cm wide and 34cm deep, starting from waist height and going all the way up to the ceiling. It's a nice little storage space with shelves that you can use to store books and such.
Unfortunately, I want to place a closet on that wall, making that nook inaccessible. I'm okay with losing the storage space in the nook.
I'm worried that because it's an empty space that's almost completely enclosed but not quite. It's hard to reach except from the top of closet. I'm worried that pests (bugs or rodents) will hide there.
Is this a reasonable concern? What can I do to prevent that? Do I need to use some filler material? Which kind?