After my previous flight lesson, I did a run around my local airport starting in my flight club's parking lot... and I kept on running and running and I looked to my left and realized I was running right alongside the runway as planes were taking off and landing. The trail looped around the runway right past the 13 numbers, then around a golf course (which I aim for when flying home from the East Bay), and back to the airport.
This was a nice 4K trail, but could easily be converted to a 5K with a few additional twists and turns. And I can also take a right somewhere and run right under the base and final legs of the 31 approach, making for an alternative 5K which can also be modified to a 2K or a 6K or a 10K (this is actually the path that is used for the annual Palo Alto Moonlight Run).
Definitely my favorite place to run, particularly on busy pattern work days!