Simple Key

   "'Simply, a simple key. It will fit a variety of locks, which is useful if you like to poke around in places you don't belong.' - Sly"

Uses
Opens simple locks, but due to its shoddy construction and the damage caused by age, it can only be used once.

There are three locations in the game that can be opened using Simple Keys. By descending order of importance, those are:
 * The entrance to Royal Waterways, which is required for game progression
 * The cave to the right of Dirtmouth, beyond the graveyard. This cave is home to Confessor Jiji, who, in return for a Rancid Egg, can summon the player's Shade, which is useful if the Shade is stuck in a hard-to-access area and holding a lot of Geo.
 * The Pleasure House in the City of Tears, along with a hot spring, Poggy Thorax and Songstress Marissa. It's also Millibelle's refuge after she scams the player. Once inside, a shortcut can be opened from the hot spring to an elevator shaft that leads from City of Tears to Resting Grounds, and also grants easy access to the topmost part of Kingdom's Edge and the Colosseum of Fools.

How to Acquire

 * One can be bought from Sly in Dirtmouth for 950 Geo.
 * One can be found in the City of Tears, in the big room with Winged Sentries and a Whispering Root just below the City Storerooms. The Key is located in one of the alcoves on the right of the room.
 * One can be found in the Ancient Basin, on the body of a Royal Retainer inside a giant dead Mawlurk.