“Windsor Castle“

Just to the west of London lies the world’s oldest and largest inhabited castle, having been a royal residence for around 950 years. First developed by William the Conqueror in the 11th century, Windsor Castle is regularly used by the Queen as a weekend retreat, as well as hosting state occasions and royal weddings. The Round Tower dominates the skyline and sits atop the oldest part of the castle, while St George’s Chapel acts as the spiritual home of the Order of the Garter – an order of chivalry dating back to the reign of Edward III in 1348. Advanced booking for the castle is recommended.
from: VisitEngland