The Cave of Time

Remember those old Choose Your Own Adventure books? This is the first one. In the book, the protagonist (you), stumbles upon a mysterious cave. Within the cave you see two portals, one that goes back in time and one that goes into the future. Spoiler alert-- if you go too far back, you get eaten by dinosaurs, and if you go to far into the future you are zapped by aliens. The book teaches that no matter which decision you make, staying in the present moment is the only way to exist.