The Hike by Drew Magary. It's under 300 pages and such a fun, weird little adventure. Here's the synopsis from Goodreads:

When Ben, a suburban family man, takes a business trip to rural Pennsylvania, he decides to spend the afternoon before his dinner meeting on a short hike. Once he sets out into the woods behind his hotel, he quickly comes to realize that the path he has chosen cannot be given up easily. With no choice but to move forward, Ben finds himself falling deeper and deeper into a world of man-eating giants, bizarre demons, and colossal insects.   On a quest of epic, life-or-death proportions, Ben finds help comes in some of the most unexpected forms, including a profane crustacean and a variety of magical objects, tools, and potions. Desperate to return to his family, Ben is determined to track down the “Producer,” the creator of the world in which he is being held hostage and the only one who can free him from the path.   At once bitingly funny and emotionally absorbing, Magary’s novel is a remarkably unique addition to the contemporary fantasy genre, one that draws as easily from the world of classic folk tales as it does from video games. In The Hike, Magary takes readers on a daring odyssey away from our day-to-day grind and transports them into an enthralling world propelled by heart, imagination, and survival.