Mayfair really is an absurdly rich area - great fun to walk around as long as you bring your own food and drink. It's also one big auto porn show with Ferraris, Lambos, Bentleys in the leading roles (the Porsche is for the au pair to drop little Chloe at ballet class).
This castle was beseiged in 1546 - the attackers dug a mine under the fortifications and the defenders successfully dug a little zig-zagging counter mine by tunneling towards the sound of digging!