Griffith Park is one of the largest urban parks in North America, and in there is located the Observatory, Hollywood Sign, Greek Theater, courts, places for picnics, hiking and many other activities.
It took us more than 3 years to do this, but since we're not an adventurous couple, it was not a priority. But the day was beautiful, the city was calm and quiet due to the holiday today, and the weather was great.
The trails are easy, not too radical (except the height!) and can be done by everyone: children, elderly, dogs etc. But since they have no signs, and there are several of them, at the very beginning we has to ask a hiker who was leaving one of them, if that trail could take us close to the Observatory (and he said yes). So off we went!
Less than 50 minutes later we were on the very top! Higher than the Observatory. From there you can see entire Los Angeles, from all sides. We stayed there for a while admiring the view and then we went down taking a different trail.
Two hours nicely spent (the time will depend on the trails you choose), breathing fresh air, sunbathing (don't forget sunblocks!) and walking. A very pleasant way to exercise and admire beautiful views!