The Griffith Park observatory recently finished a long shutdown for refurbishing. It's now available for visits -- you can find info and website on any search engine. need tickets in advance to ride the shuttle from some remote lots.

After that... you can drive through the festival of lights in Griffith Park (after sundown) -- it's a bit cheesey, but good cheesey.

Once that wonderment is finished -- head up to Ventura. It's a cute little town on the coast, although most people just pass it on the 101 without knowing what's beyond the freeway exit. Spend the night there, grab some dinner.

Just a thought.

p.s. planetarium tickets sold separate on 1st come basis once you get up to the observatory.