King Charles III's impressive property portfolio extends up and down the UK, including the 775-room Buckingham Palace in London and the idyllic Highgrove House in Gloucestershire. Balmoral Castle is his most famous Scottish residence, but there's also Birkhall and Holyroodhouse. This castle is where King Charles is currently staying, marking the start of his annual summer break. It was once home to The Queen Mother, and it has been widely reported that the late monarch purchased the property for anywhere between £1 and £100 in 1952. While King Charles and Queen Camilla regularly visit the castle, it has been open to the public since 2002, after the Queen Mother passed away.