Gamebook writer Joe Dever is most famous for his Lone Wolf series, highly ranked among "choose-your-own adventure"-like branching novels with role-playing elements. But he also created a series I remembered only dimly from my 1980s British childhood: gamebooks that were fully-fledged multiplayer grid-based dungeon crawlers. Combat Heroes contained not only a page for facing each cardinal direction for every square in the dungeon, but variants of each showing every possible orientation and position of your adversary for each player-vs-player pair of books, including them hiding behind objects. There's an elegant if intimidating system for determining which page to jump to. On top of that, somehow stuffed into the ~400 pages, each book includes a single-player quest replete with items to pick up and use.
The books were and are amazing examples of clever, carefully optimized design, though their complexity was a barrier to my 9-year-old brain and, notwithstanding the ingenuity, the dungeons were very small. It amounted to a gamebook simulation of a fight in a basement. There were two pairs of books (i.e. two battles and four single-player adventures): White Warlord and Black Baron, then Scarlet Sorcerer and Emerald Enchanter. These appear to sell for hundreds of dollars each on eBay.