Topsy Turvy Achievement
Unlock the Inverted Castle.
Castlevania has four possible endings and it is possible to end the game without unlocking the Inverted Castle. To unlock the Inverted Castle, you must acquire the Holy Glasses from Maria. With these equipped, proceed to the fight with Richter. If you have the Glasses equipped, you'll see an orb floating around the room with Richter. Focus your attacks on the orb and destroy it. Once you do, you'll free Richter from it's spell and unlock the Inverted Castle.