Lost Precursor City

The  is a location in the Crystal Hollows where the Sapphire Crystal can be obtained. Six Automaton Parts are required to claim the crystal, each randomly obtained by killing Automaton or opening chests in the Crystal Hollows. Delivering all six parts to Professor Robot will unlock the door next to him.

Trivia

 * If you right click on the blocks in the door to the Sapphire Crystal, they will disappear although the Crystal will not appear until you have given all 6 parts to Professor Robot