This famous London landmark was commissioned by King Edward VII in memory of his mother, Queen Victoria. It is now a Grade I listed building. In the past, it served as residence of the First Sea Lord and was used by the Admiralty.
Interestingly the structure is asymmetrical; when viewed from the Mall, the right wing of the building has one floor more than the left one: below the cornice there are three on the right, but just two on the left. I was sitting on the Trafalgar Square side, however, so this detail isn't apparent.
The building has now been sold to a private developer who will be making it into a luxury hotel - you can see their plans here:
Or you could find out more about the building on the Historic England page