From the Bethblog:
Inside the Vault presents one of our level designers, Daryl Brigner.
What’s your job at Bethesda?
I’m a Level Designer. I design the layout for specific areas/dungeons. This usually consists of where enemies are, where and what the loot is, and what the basic flow of the dungeon is.[…]
Any other hobbies and interests? What do you enjoy doing in your spare time?
Playing games, watching movies, and, believe it or not, making levels for other games. I’ve recently made a small map pack for Portal called Ren_Test3 It’s been featured on our site here along with my previous map. I have a lot of fun making those Portal maps because it’s less about the aesthetics and more about the puzzle design.
I’ve also done a few mapping tutorials for Half-Life 2, and will probably do some more of them in the future. They are four beginner tutorials and can be found if you just Google “Renstrike Mapping Tutorial”.