try getting a tour at the NASA Jet Propulsion Laboratory, they also have an open house once a year, its free but ticketed, they sold out in a couple hours last year so you have to be quick
you can also just drive on mulholland and/or go through the mountains
there are a ton of hiking Trails so if you're into that you should check it out
if you want a nice beach, dont bother with santa Monica, just go a bit North. zuma beach is pretty cool
for stuff like Halloween and Christmas it's nice to see how People decorated their houses (at least for me it was, because we dont do it that much in Germany), there is a neat street somewhere around 1606 Carlyle Ave, Santa Monica, CA 90402, USA but i dont really remember exactly where