[Back cover] The Underdark Adventure Guide is a world-neutral, standalone guide to adventuring in the strange, alien world of the underdark. The underdark is far more than just dungeons and caves. It is a veritable underground continent, populated by advanced civilizations, ancient ruins, sunless seas, alien magic, bizarre creatures, and the horrid denizens of the gloom. The standards of the surface world hold no sway in the underdark, and its mysteries, ferocity, and danger will challenge even the hardiest of adventurers. Underdark adventures are easy to integrate with an existing campaign, as the very nature of the underdark lends itself to layering -- simply arrange for the discovery of a subterranean portal, and the land beneath your existing campaign has a new life. The Underdark Adventure Guide includes everything you need to create a compelling underdark campaign: New character options for underdark explorers, ranging from new feats and adventuring gear to prestige classes specially tailored to the underdark races: drow, derro, duergar, svirfneblin, and troglodytes. More than a dozen new monsters native to the underdark, plus a variety of specialized plants and bizarre funguses. Extensive guidelines and world-building advice for constructing your own underdark region. A dozen fully developed points of interest. You can use these piecemeal as drop-in locations in your existing campaign, or use them together as a fully-developed, integrated underdark region.