Salton Sea is not technically LA, but is a by-product of its history and my first-choice escape from the city: one of the world's largest inland seas and lowest spots on earth, a man-made lake in the midst of the Colorado desert, a resort area in the twenties turned in one of the worst ecological disaster of the past century.
Old Bat cave and filming location in grifith park in los angeles. there is a nice hike to get to the cave, and it is a unique history to the place imbued with Hollywood remnants.