This piece of art is called ‘The Breastplate’. It’s located at the Oudekerksplein, near the famous Oude Kerk (the old church), in the centre of Amsterdam’s red light district.
After doing some research I learned that The Breastplate was placed one night, without permission, by the ‘Unknown Sculptor’. Since 1982 the Unknown Sculptor seems to have placed several sculptures in Amsterdam. The City of Amsterdam has become their official owner, provided that the identity of the Unknown Sculptor will be kept a secret.