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Hire kayaks https://www.questkayak.com/ (Don't forget sun screen!)
If the weather's good, go to the beach! Lewes Beach is fine, or there's a beach on the oceanside in Cape Henlopen State Park. (Don't forget sun screen!)
Visit the Zwaanendael Museum: https://history.delaware.gov/museums/zm/zm_main.shtml
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