Megadungeon Hall of Fame Post: "The Megadungeon and the Horror"
The same is true with blog posts. There are a few blog posts that I find myself going back to in order to read again and think about contents. Beedo's (Dreams in the Lich House) post, The Megadungeon and the Horror, is one such post. Beedo compares and contrasts the typical characteristics of a megadungeon (large areas, multilevel, factions, sparse details) with the typical characteristics of a horror scenario (atmosphere, detail, a careful buildup of tension).
Given the challenges of creating a horror-based megadungeon, Beedo suggests incorporating small, detailed, set-piece areas with weird, powerful, horrifying monsters to create a sense of horror. While that doesn't create a horror-based dungeon, it can create some horror-based sessions within the larger megadungeon campaign. From my perspective, it also creates some additional variety and contrast for the GM and players.