Windsor Castle is the oldest castle that has been continually inhabited by royals in Britain. It was built by William the Conqueror in 1080. It was intended to guard the western approach to London.
It is huge and could spend a few hours here. There is airport security because the Queen does live her and visits on weekends.
You can also book tours of the tower. I didn't get a chance because traffic was so bad on the way so we were late and had a tight schedule.
Be prepared for bad traffic during the week on the way.
A huge ceremony takes place every year at Windsor Castle for the Garter Service that dates back to 1348. New knights take an oath and are invested with the insignia of the Order of Garter. There are only 24 knights and one can only be replaced when one has passed away. The Queen and the knights wear blue velvet robes, black velvet hats and white plumes (feathers). Also the Military Knights of Windsor who are retired and live in Windsor Castle take part as well. It is a great chance to see the royals!
I like that Windsor feels more that it is a living community rather than a museum. There are almost 100 people that live here.
A limited number of tickets is available for members of the public to stand inside the precincts of Windsor Castle and watch the procession to St. George's Chapel. Apply between 1 Jan and 1 March by sending an email to Garter day firstname.lastname@example.org.
This is a service so its best to be respectful and quiet while it goes on. It is also a a great day out. Get there for 11 am to join the queue but they do not pack people like sardines so you can bring a camping chair and a pack a picnic (not a large basket) and enjoy. It is all very civilized. Also its free!
For more information please see this link.