California Science Center is a free hands on museum. It has several exhibits dealing with inventions, biology, and my favorite, Air and Space. There is an Imax Theater and special exhibits which require an entrance fee.
The Air and Space section explores Air and Aircraft, Humans in Space, Mission to the Planets, and Stars and Telescopes. You can also slip on a pair of wings and go into a wind tunnel or work the controls from the cockpit of a Bell-47 Helicopter. There are also an A-12 Blackbird, Bell X-1, and a T-38, among other aircraft, that you can explore.
This is only the tip of the iceburg. There are several exhibits to explore that will keep you busy all day. Not bad for no cost. To see more of the Top 10 Free Attractions, go to the Los Angeles section of the NonRevWebsite.com To see free attractions form around the World, go to NonRevWebsite.com.