Dungeon Levels
Dungeon levels were once considered the primary feature of the game environment but don't have the same significance today. To quote the very first instruction the White Box has for DM's, "First, the referee must draw out a minimum of half a dozen maps of the levels of his "underworld, ..." Descending into a lower dungeon level was meant to expose characters to a higher level of danger, and a feature of dungeon design was some sort of trick or trap that would deposit them in lower levels against their will. For me and probably many others who started with the Basic Set, the Sample Cross Section of Levels for Stone Mountain on p38 of the Holmes Basic Rules was the archetype. The dungeons themselves used to be the story. Today the story might move through a dungeon, but only in service of a plot that exists beyond the dungeon. I miss old school dungeons. (I don't miss the old school rules.)