Tokyo Imperial Palace
The Tokyo Imperial Palace was built on the grounds of the former Edo Castle. The Fushimi Yagura of the castle dates back to 1659 and the famous Nijubashi area dates back to the same century. There is also a large area of imperial pines. You can see all of these from the outside, but to enter the actual Imperial Palace grounds, you must reserve a spot on one of their tours which can be done on their website.