Portal 2 - Constant Motion - Fan Made Level
Cave Johnson here. If come face to face with a turret and it starts singing opera that is because a so called cave man reprogrammed it. We will fix all turrets soon and have already fixed the reprogrammer. So, if when you stand in front of a turret it doesn't shoot you down there and then either poke it with a stick until it does or find an American turret that doesn't know a single word of Italian and will never trade bullets for opera. Chariots. Chariots.
18th Level created I created using the Portal 2 perpetual testing initiative level editor. My steam ID is psn_girv24601 if you want to play any levels for yourself, search for Achievement King.