Anna's Archive provides a lot of large format torrents covering large swaths of a virtual library as well as direct access to specific titles. If there's one thing or type of book in particular you are looking for idk how well the large format torrents cover those situations though.
I didn't know about Anna's torrents and got super excited, then looked it up and got really confused. How am I supposed to know which of these torrents hold which books?! There's probably a guide or search I didn't find, but I'm genuinely unsure how to use these thousands of torrent files.
I mean, given the mission to preserve a large amount of humanity's knowledge, that's bound to be a complex system, so I'm definitely not surprised it isn't immediately straightforward. A guide would definitely be useful, though.
Anna's torrents are mostly meant for archival not user access. You could probably piece together what books are where bases off their identifier but I haven't used it enough to really say yea or nay, I just know the site exists.