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This stone house, reconstructed by the (in)famous urban planner Robert Moses, is a replica of a 1699 Dutch farmhouse. A permanent exhibit explains the Battle of Long Island (what Brooklyn was known as c 1776), which includes period clothes and weapons. Concerts and other cultural events (author talks, tastings) are held regularly, and there's a great playground for kids, too.
If you happen to pass by outside of the posted visiting hours, give them a call. If someone's inside they'll usually be happy to let you in.