1. Piranesi by Susanna Clarke - not much to add than everyone else but yes loved this book read it immediately
2. The Starless Sea by Erin Morgenstern - quite Neverwhere in it's subject matter, however after a slow 50 -100 pages it becomes quite addictive. Beautifully written with dozens of literature reference Easter eggs. Also the author credited Dragon Age: Inquisition as an inspiration so it's very much a nerds delight.
3. Roadside Picnic by Boris and Arkady Strugatsky - read based in recommendations here, and yes while I did like it it didn't grab me in the same