The best way to get here is to come in from Park Boulevard on Village Place, which is the first street off Park Boulevard north of the Reuben Fleet Space Museum. Park in the big lots either to the right or left as you come in, and head towards the fountain at the Reuben Fleet Museum. The Natural History Museum will be on your right. Go to the other side of that museum, cross the street and you will be at the Casa del Prado.
Click to see a Balboa Park map. The Casa del Prado is building 15.
If you’re not sure how to get to Balboa park, here’s the location in Google Maps.