Can't post a picture, but basically we had a long wall in a high ceiling room, high skirting boards, picture rail and a big radiator in the middle. And lots of books. We had shelves built in that went up to the picture rail, that sat on a plinth the same height as the skirting boards, that went up and over the radiator. We added some sockets so we could plug in lights (there are many more good rechargeable lights on the market 10 years on, so you might not need this) because otherwise we'd have had a wall without lights in a room with no overhead lights (and we weren't about to gouge out the ceiling to install). The shelves were on pegs, so we can move and change the heights and gaps, but the uprights are obviously evenly spaced.
The thing that I worried about - would it look odd with the edge of the stack visible from the side as you look in through the door of the room - is no problem at all. Everything - walls, shelves, radiator, skirting boards - are the same colour, so it all melds together. I've thinned out books over the years, as well as buying more, and now the shelves house lots of books as well as pictures, ornaments, vases - it's a bit more Instagrammy (blush - lockdown did it to me) and considered.
Sorry, long post - but just to say, really, that you don't need a recess, but do build so that it fits in with the existing bones of the room; and you might like to think about breaking up a long wall of bookshelves with pictures and ornaments.