Spooky City at the Museum of the City of New York
Time Out says
You can wear your costume to the Spooky City party at the Museum of the City of New York, or you can make a mask at the event. Then you and your little ghouls can trick or treat at a haunted scavenger hunt that will take you through the museum, where you'll enjoy spooky tales and tasty treats. The event is free with museum admission, but it's suggested you register online here.