So many indie puzzlers start with a pretty simple premise, like "what if you could put boxes inside of other boxes," and end with absolute mind-bending madness like "I have seven layers of boxes and they seem to have started infinitely recurring."
Such is Patrick's Parabox, a Sokoban box-pushing game that has as its unique feature that you can push boxes into spaces carved into other boxes. Over the course of 350-some well-tutorialized box puzzles, Patrick's Parabox continually introduces new ideas into its puzzles. Eventually, as I'm sure you'll realize, it becomes boxes within boxes within boxes... all within a larger box, accessed perhaps from a door within the smallest box.
Patrick's Parabox also sports a melodic electronic soundtrack from Priscilla Snow, also known as ghoulnoise. That alone ended up being worth the price of entry, for me. I hadn't heard of Snow prior to the game, but I'm now a fan—you can find that soundtrack on bandcamp.
You can find Patrick's Parabox on Steam and on Itch.io. You can try a free demo at either place.