The first person to make World 1-1 loses.
Bethesda has released their creation kit for Skyrim via Steam, meaning you're free to create whatever you want to your heart's content using their level design tools. The engine Bethesda has created isn't without its faults but it's capable of so much lushness and variety, so let's not see either plumbers or blocks (at least with the first round of mods) for a little while, eh budding level designers?
Bethesda has also released what can only be considered a "Prettification kit" to go along with their Creation Kit in case you needed higher fidelity for your Skyrim gameplay and modding experience. These are the system specs for the whole ball of wax from Bethesda:
Make sure your system requirements exceed Skyrim’s recommended specs before attempting to install, including Windows Vista or 7 operating system, a minimum of 4GB of system RAM, and a DirectX 9.0c compatible NVIDIA or AMD ATI video card with at least 1 GB of RAM and the latest drivers.
Seriously though, I'm really looking forward to what you guys start creating out there. We've got some true mad scientists who I'm certain are going to make things both wonderful and that can't be unseen.