When people talk about biking of any kind in Forest Park, they are likely talking about Leif Erikson Drive. This nearly 11 mile long gravel doubletrack serves as the main artery for two wheels in Forest Park. Most of the other bike-legal trails connect to this gravel road.
Parking is at either end but the northern trailhead has a larger lot. However it's a little out of the way. The southern trailhead is at the end of a neighborhood street and so it can be tight and cramped.
Never super steep, this can be a leisurely stroll after work or school, or a way to get in some miles during the rainy winter.