Atlas Obscura is one of the largest, most well-known and most impeccably awesome archives of amazing places, foods and experiences in the world.
Here is their list of places to see in the First State, Delaware! Featuring such sites as: Miles the Monster, a concrete behemoth bearing a NASCAR racecar outside Dover International Speedway; The Cannonball House, a house with a British cannonball in the side; and Nemours Estate, the largest French-style formal gardens in North America. How many of these wondrous places have you been to?
Note: Some of these you cannot visit or see anymore, which have been marked with (Permanently Closed). So therefore, if you haven't already seen them, I don't know if you'll ever be able to completely finish this list.
Note 2: This is as of October 7, 2023. Sorry future people, there will definitely be more that can't be added.