The first part of the walk can be a little tricky, though since we'll all be descending, somebody who knows can point out the trailhead. You'll traverse the northern edge of the park, beneath Mt. Chapel (little more than a water tank, really), until you reach paved - but car-free - Mt. Hollywood Drive. From there, it is a 1.9 mile walk downhill to the observatory.
Major cautions are water and heat; poison oak; getting lost, since it might be late; and missing the last shuttle.
View Big Parade Return Via Griffith Park in a larger map