Third Courtyard (Rear)
From the Super Mario Wiki, the Mario encyclopedia
Third Courtyard (Rear) is a location in Super Mario Odyssey. It is located in Bowser's Kingdom, connected to Third Courtyard (Front) via a spark pylon. At the start of this area is a Checkpoint Flag between two torches. After some stairs, Mario reaches an enclosed area with two Spinies, three ? Blocks, and a rainbow treble clef on the left. The middle ? Block is a Coin Block. Above the middle ? Block is a Hidden Block containing a Heart. If Mario touches the treble clef, Notes appear in the pen. Collecting all of them before time runs out makes Power Moon #18, "Taking Notes: Between Spinies", appear in place of the treble clef.
To the right of the pen are three Coin Rings over a pit. After that is a Stairface Ogre. Once Mario defeats it, Power Moon #1, "Infiltrate Bowser's Castle!" appears from behind. After collecting this Power Moon, the doors ahead open and stairs rise, taking Mario to an area with crates and a spark pylon which takes him to the Second Courtyard. In the crate section, Mario is able to get up onto the roof, where he can find some regional coins, as well as a Pokio on the side. Mario can capture the Pokio and poke the hole in the middle of the wall to reveal Power Moon #21, "Poking Your Nose in the Plaster Wall".
After opening the kingdom's Moon Rock, a second rainbow treble clef appears over the roof, on the side of the courtyard. Mario can touch this treble clef for notes to appear on the wall, which he must use a Pokio to collect. After collecting all of the notes in the given time, Power Moon #54, "Taking Notes: On the Wall", appears for Mario to collect.