I work as a Research Engineer for Brookhaven National Laboratory in the Physics Department X-Ray Scattering Group. Our group has three X-ray Beam Lines at the National Synchrotron Light Source. I am the head of the technical staff in our group. I am responsible for keeping the experimental equipment running, mechanical/electrical/electronic design (from widgets to whole beam lines), administering all of our groups computers, and supervising the technical staff. I have a formal education in mechanical design, all the rest of what I do is self-taught or was learned on-the-job.
There is a never ending stream of challenges, and they _pay_ me to work.