Last night my girlfriend and I stumbled into the LA Live Steamers Halloween Haunted Train Ride in Griffith Park. It's $5, and was way, way, better than I expected - GO NOW. note: small children may actually be pretty scared!
The LA Live Steamers museum is about a mile east of Travel Town- Travel Town has full size trains, and LALS has smaller model trains - that are still large enough to take you on rides. It's separate from Travel Town and pretty easy to miss.