During the Feltrite Sample job, talk to Kvasir to start this one. Get back in your buggy and follow the mini-map to Dead City Streets. This is a pretty tough section, so be prepared, you have to fight two mini-boss sized enemies. Eventually you'll get to the Dead City Center.
When you get in the Dead City Center, you'll see a switch that won't work leading to a room you can't get in. Shoot the explosive barrel in that room to burn the wood blocking the entrance. You can now open the doors down the escalators, but there will be another large wave of enemies.
When you come to the Rocket Launcher, it's boss time, so save. Aim for his electric blue weak points. The machine where you got the rockets will keep making ammo for when you run out. His health is in the upper right corner. After you beat him, a new path will open up to the left. Eventually you'll come to the defibrillator upgrade, and get the It's Alive achievement. It will also trigger more enemies. Head back to the Wasteland and return to Kvasir.
Collector Card: Slime Mutant - When you walk into Dead City Center it's ahead to the left on a table with a lantern.