Personal Experience: The Bridle Trail really comes as a surprise if you happen to stumble upon it. Basically being located in the heart of the city, it's not the type of place you'd expect to come across in this area. This trail is located west of Route 163 in Balboa Park, and in fact, during parts of the trail you will walk right alongside the freeway and underneath the Cabrillo bridge! You can access the trail from several points including along Balboa dr. & 6th ave. and a spot several yards north of the lawn bowling site.
I love this trail for so many reasons: the tranquility, unique beauty to San Diego, the flower fields in the springtime, fresh air. It all evokes clarity and peace of mind. I would not recommend going alone as you will occasionally come across a suspicious person or two. Balboa is notorious for lewd activities, such as sexual assaults and drugs.
Update as of May 2016: I have noticed the trees are dying.
Update 2019: Most of the trees have now been cut down. This page may have to become part of our lost history section at this point. Redwoods are not meant for this weather, I was told. But how did they survive for so many years up until this point? They seemed to be thriving even 6 years ago! I am lost.
The hike is actually right along the freeway much of the time:
One day there was a bird that I swear escaped from the zoo which is right next door!