I have made the drive to Gen Con many times, and it’s about three and a half hours. It’s no grueling cross-country trek, but it has proven boring even with a decent music playlist — especially when I’m driving solo. Having a good audiobook playing made it feel like 15 minutes.
The Plane Above is the next 4th Edition D&D supplement that focuses specifically on the Astral Sea, denizens of the plane, a wide variety of locations found there, campaign ideas involving the plane and a handful of new monsters that can be found in the Astral Sea.
The latest 4th Edition Dungeons & Dragons supplement from Wizards of the Coast is simply titled Underdark, and it contains all kinds of information and fleshed out details on the entire realm for which it is named. This book is along the same vein as The Plane Below book on the Elemental Chaos, but the Underdark is a subterranean realm just beneath the surface of your game world and so will always be more accessible than the other planes to your players and their characters.