Aliens in Tamriel is a level mod done using the Elder Scrolls Construction Set from Elder Scrolls IV: Oblivion. The level is in the form of a quest and revolves around gathering information about an alien invasion in the game world. In Cheydinhal, Milton Nicknesse says he saw aliens inside a mountain but no one believes him. Fearing that the aliens will destroy them all, he asks the hero to investigate the mountain and bring back proof of the aliens' existence. Upon adventuring to the mountain, the hero finds a cave and enters to discover that it is actually an alien base with ships and humanoid aliens.
Inside the cave there are two floors. The top floor has a large room that is open to the outside and is where spaceships enter and leave the base. The lower floor however is the living area and the alien leader. In the kitchen, the hero can release a caged alien creature that then fights alongside, thankful for not becoming a meal. On the leader's desk there is an alien technology that can be retrieved and shown to Milton as proof of the alien presence. However, the more bold adventurer can attack and defeat the alien leader who was communicating with the mothership via a large screen. Killing the leader bestows an alien weapon to the player that is also proof.
I was urged by several not to make a level in the Construction Set because of difficulty to use and bug issues. However, I found the editor to be quite easy to use and navigate. I agree that there are some bugs with the program, but by utilizing patches and additional tools, bugs became virtually non-existent for me. I was impressed by the systems the editor has in place for constructing levels, and I understand now how Bethesda can create such immense virtual worlds. This experience has had a large effect on how I view level construction and scripting.