What used to be a niche event for history buffs and fantasy fans is now trending big—and young adults are driving the hype. But what’s behind the sudden obsession with all things medieval and magical?

The Silvan Elves from the Woodland Realm, like Legolas and his father, Thranduil (Lee Pace), only begin their exodus after the War of the Ring, but, during the conflict, also have their hands full.

“Yes, an elf,” the girl said. “Or to be exact, a woodland elf.” Wilson sat still on his decrepit wooden chair, eyes transfixed on her. He was approaching 89, and while he was slowing in ...