This is the place you go to for a free guided tour of the Dover historic district. The guides dress in 18th century (?) garb and they take you out on a 45 minute walking tour of the square.
Our guide (I believe her name was Anne?) was amazing! The whole tour was very captivating and it was evident that our guide was very passionate about Delaware history. We went there on a Wednesday afternoon, and my wife and I were there only ones there. The whole tour is wheelchair accessible, although, you have to be careful at certain points due to uneven surfaces.
On the whole, I would strongly recommend taking the tour. Learnt a lot about Delaware history in those 45 minutes.