Cibeles Square, Madrid
As you are in Cibeles Sqaure looking towards Puerta del Sol, the big building at your left with the golden sphere on its roof houses the main offices of the Banco de Espana (Bank of Spain).
You can visit it inside, here is where the money lives :-))
But you can admire its wonderful facade. In the main gate at the Alcala Street (neatr the entrance of the subway pass) you can see one of the few remaining republican badges in Madrid), at the top of the building. You will recognize it by the little castle on top of it. It was put there during the Civil War and never removed...
The Plaza de Cibeles is a very busy roundabout with a fountain in the middle. At the south eastern side is the Palacio de Comunicaciones (1905-1917). This impressive building houses the General Post Office of Madrid.
All night buses go from here. They are called "buhos." If you know where you are trying to go, then definitely take one cuz they are way cheaper than taxis (or free if you have an abono!)
In the middle of the square - watch the traffic - is the fountain of the Roman goddess Cybele. She seems to be transported in a farm cart of the 18th C!
This beautiful building located in the Cibeles Square houses the central Post Office of Spain. If you desperately need some stamps on sunday, this is the place to go.