If you are visiting the Los Angeles area during Halloween you must see the West Hollywood Halloween Parade! It is the largest Halloween street party in the world. It is every year on Halloween day (October 31st.) Btw the admission is free, the parade includes a free live concert. The parade usually runs from 6 p.m. until 11 p.m. and after the street parade is over then most nearby bars and restaurants continue with the festivities until closing time. It is really fun and worthwhile to go at least once in your life to see it. Prepare yourself for a crazy, crazy night 😉
My advice is if you drive to come there early, around 4:00 PM, to get a good parking spot. Later on during the night the parking is nearly impossible to find. And also the traffic is terrible. So plan in advance.