Things to do indoors in New York

I’ll be on holiday in New York from the 18th to the 27th of september, together with my parents. Seeing what rain and thunderstorms Ivan is bringing with it, I’ll have to plan a lot of indoor activities.

You have to know that this will be the 7th year on a row that I will visit NY city. Never for shorter than a week, and my longest was a month. So I’ve seen just about all museums, historic houses and shows on Manhattan and in the other borroughs.

My question to you is: do you know any of-the-beaten-path indoor activities to do in New York?