As GMs, we draw inspiration for ideas - and life ideas whole-cloth - from books, movies, tv, and mythology. I propose another valid source: the lyrics and album covers of many Metal bands. Below are linked some of those mentioned in the episode, and a few others.
Iron Maiden, "Sun and Steel"
Iron Maiden, "The Wicker Man"
Iron Maiden, "The Duellists"
Iron Maiden, "The Prophecy"
Judas Priest, "Tyrant"
Judas Priest, "Bloodstone"
Judas Priest, "The Sentinel"
Type O Negative, "Wolf Moon"
Rainbow, "Man on the Silver Mountain"
Bolt Thrower, "Granite Wall"
Iron Maiden, Somewhere in Time
Iron Maiden, Brave New World
Iron Maiden, Powerslave
Bolt Thrower - various wallpapers