Hordes of the Underdark is the second expansion pack for BioWare's popular Dungeons & Dragons role-playing game, Neverwinter Nights. The original was a combination of a single-player role-playing game, an editing tool to create your own custom adventures, and a multiplayer role-playing client. Sure enough, Hordes makes additions in each of these areas. The expansion's substantial single-player campaign should last most players 15-20 hours, and while it doesn't have many surprises, it does offer some worthwhile new features that Neverwinter Nights fans should enjoy.