Huge cypress trees and migrating birds
Trap Pond State Park is a spectacular wetlands park near Laurel, Delaware and, to me at least, seems more like something you'd find in Louisiana or Florida than in rural Delaware. The park preserves what were once extensive marshes in the Sussex County area and is home to tons of bald cypress trees. For those not botanically-inclined, bald cypresses are those mammoth trees with the bulky roots that you see growing out the water in places like the bayou or the Everglades.
Given that Trap Pond State Park is a marshy area, the most popular activities are naturally boating and bird-watching.