The Lost City - 26 - it's name is generic because it was first
Desert of Desolation - 24
Isle of Dread - 27
Castle Amber - 24
Red Hand of Doom - 19
Lost Caverns of Tsojcanth - 11
Many on this list where the first adventures of their kind. The Lost City was the first lost city adventure, Isle of Dread was the first "explore a new land" adventure, Test of the Warlords was the first "build a kingdom" adventure, Castle Amber was the first officially based on a novel series, Desert of Desolation was the first novelistic plot driven adventure.