Hampton Court, England
The Castle itself is only viewable on a guided tour. The Palace was built starting in the 1400s. The kitchen and chapel, to me, were the most interesting parts, although several of the period rooms were interesting. In some cases, your interest may vary depending on your guide (who is in period dress) can be fun. It is an easy trip from anywhere in London. It’s fairly close to Heathrow, and a person on our tour did ask why they built the castle so close to the airport.
The gardens at Hampton Court are extensive and well-tended. There is a kitchen garden, a sunken garden (with a waterfall), a hedge maze, Rose Garden, and a Dutch Garden. Further, there is a long wisteria arch that is glorious when they are blooming.