The second expansion to Neverwinter Nights, Hordes of the Underdark takes players to Undermountain, which has been contained beneath Waterdeep ever since it was created. Now the creator has disappeared and the monsters are fighting for supremacy as well as coming out into Waterdeep.
On top of that, the Dark Elves make stealthy attacks. These Drow are killing off various wealthy and powerful people in Waterdeep as they sleep. Waterdeep cannot handle all these problems alone and so they put out a call for adventurers.
This expansion features sixteen new creatures, four new tilesets, six new prestige classes, over fifty new feats, over forty new spells, new music and voices, new functionality in the toolset, 20+ hours of gameplay in the main campaign, and characters can now reach level forty.