What started out as a niche storytelling adventure in 1974 has now been experienced by more than 40 million people worldwide. The fantasy role-playing game Dungeons & Dragons has leapt from tabletop boards to video games, livestreaming and now a convention of devotees.

Adweek got to experience the D&D phenomenon first hand earlier this summer at the Founders and Legends convention, where we talked to celebrity superfans including Joe Manganiello and Deborah Ann Woll, as well as the game’s writers, artists, rule-makers and designers.