Usually we stop at the Palomar Observatory because it has a nice big lot of taking pictures. The Observatory itself is pretty interesting to visit (it's the facility that started the whole Pluto-is-no-longer-a-planet debate) and the twisty roads (S6 and S7) were built to move equipment for the Observatory's construction. Now it's just a weekend fun-run
I dug up an old video of a Palomar downhill run I filmed last year. The video is completely raw and unedited so I recommend you mute it as soon as it loads up or all you get is wind noise. I had decided to drive up the mountain on a busy weekend just for shits and giggles ~ my sister is holding our Sony snapshot camera out the moonroof so it's neither excellent quality nor super-steady. Finally, note the video was taken in late September last year; just days before the 2007 SoCal Wildfires ripped through the area and torched all the trees.