Bayfront Park in Menlo Park is a part of the Bay Trail regional trail network and is built on an old landfill. The hillocks in this park are literally big piles of garbage that have been covered over with dirt and grass.
The park is crisscrossed with gravel and dirt trails, with a gravel perimeter road around the whole thing. There are also remnants of paved roads that used to be used by the trash haulers.
The park juts out into the salt flats of the Bay.
This city park is just two miles from my work. I've done all of the trails in this park on a fixed gear bike, so it's not exactly challenging mountain bike terrain, but it's okay for a quick lunch break. This park is a popular lunchtime walking area for workers in the nearby office parks.
No map is necessary -- if you get lost in this tiny park, just climb the highest hill in the park and look around.