San Dieguito County Park is a vast 100-acre park located near Rancho Santa Fe, one of the richest zip codes. It's a mix between a multi-use park and a trail park. The best route there is El Camino Real. It's more scenic, and you'll enter by the pond. But if you're coming off the freeway, it wouldn't make sense. Parking should never be an issue, even free spots should be available.
If you enter from El Camino Real, you'll be greeted by dozens of ducks hanging out by the ponds and water fountains. To the right is a butterfly garden with a mini trail through some plants. This area alone is worth the trip. It's a nice tranquil spot. Cars will come and go, but there are never many.
However, you came for the main attraction, but reaching the top can be quite arduous at times. You'll either climb dozens of steps or traverse a steep incline.
Once at the top, you'll be surrounded by beautiful valley views. There are several lookout points to visit and suspension bridges to walk across. There's nothing like a wooden rope bridge. You could spend a few hours exploring the summit.
The only downside is your adventure is ruined by the road that loops around below, the cars driving it, people playing sports, and random buildings up top. There's nothing wrong with these things, of course, but it ruins the immersion of escaping. I also found myself lost at certain points, which is hard to imagine, given the park's size and amenities. There are maps at the top, but there's nothing on the surrounding trails.
San Dieguito County Park is definitely worth a visit, and there are many things you can do here. If you're coming with your family and you disagree on what to do, there are plenty of options for everyone to do what they want. If all else fails, you can always have a picnic.