Horse Guards Parade in Westminster

You're standing on Horse Guards Parade, a big open parade ground just off Whitehall in central London. Start by looking east. That's the Horse Guards building, designed by William Kent. Its arches are usually how people walk in from Whitehall. Now spot the clock above it. The number two has a black background. The popular story is that it marks the hour King Charles the First was beheaded, at the Banqueting House across the road.