J.R.R. Tolkien's The Two Towers includes books three and four of the six books that make up The Lord of the Rings. Its fun to re-read old favorites because I find new things in the story that didn't necessarily appear the first or even the second time through. I won't get into specifics about those things, both to avoid spoilers, and because many of those things are just a feeling or a sense that I don't remember in previous readings.
I've also read volume 1 of The History of The Lord of the Rings [part of the larger series; The History of Middle Earth, which has something like 12 volumes.] I read the first volume years ago and I'm currently reading the second, so more on that later, but I will say here is that Tolkien spent years drafting, spit balling, brain storming, outlining, and revising the LOTR. The final story is extremely complex, cross referenced, and maybe most importantly, underlain by a backstory so thoroughly wrought that the book reads almost like a history of real events that may have taken place in our own history or one very similar to our own.
Warning: What follows includes some information from the story, which some may not want to read, if you're trying to know nothing of the storyline beforehand.
Book 3 follows the adventures of a portion of the fellowship, across Rohan and eventually to the tower of Orthanc. Book 4 catches us up on the travels of the ring after the breaking of the fellowship, which takes Frodo to the second of the two towers, in Minus Morgul.* This method of tracking different parts of the story exclusively makes it a little harder to keep track of what is happening consecutively elsewhere in the story, but it does a great job of building suspense and keeping the reader engaged.
The Two Towers doesn't just move the story forward, it includes major plot drivers in the overall struggle between our heroes and the evil they're fighting against.
Yeah, read this book. Its one of my favorites.
* I've never been completely sure which two towers the title referred to, and apparently Tolkien was a little unsure on the subject after having come up with the title. He later settled on Orthanc and Minus Morgul, and even did a drawing for the cover, which is now used on certain re-prints. yeah, that's the one I used, even though that's not what my copy looks like