Windsor is a very lovely small town. You can't miss the castle. Take your time for a visit, as there is lots to see. After a security check you can pick up an audioguide and then your tour begins. You can start at Queen Mary's doll house, but also at the St George chapel, where recently Prince Charles got married. The highlight for me was the staircase of the castle and the grand hall. It is very impressive and still in use. It is really one of my favorites, and in easy reach from London Paddington/Slough. Windsor castle is worth a visit, and while you are there, you can also visit the town. There are many shops and plenty of places to eat or have a drink. And you can see a play at the Royal Windsor Theatre to finish your day.