Schlüssel or "Key" in English, is a puzzle by the infamous "Roger D". Roger D is a mysterious puzzle designer from Germany, and his actual identity is known only to a few. Roger is known throughout the puzzling world for his extremely difficult and high quality machined aluminum puzzles. Roger's puzzles are produced in relatively small numbers and are highly collectible, they are also sold with no information as to the objective of the puzzles and this is classed as adding an extra degree of difficulty to them.
The Schlüssel puzzle is an aluminum puzzle with a gold-colored key protruding from the top. The initials of the designer are cleverly engraved on the top to look like a key itself. The objective is to unlock the puzzle by removing the key. An eloquent solution!