Castle Courtyard (also called Castle Gardens) is in the back of Princess Peach's Castle in the games Super Mario 64 and Super Mario 64 DS. There are 4 signs and a fountain. When you have no stars, there's nothing, after a Star, a Boo will be in the hallway and group of regular-sized boos will appear in the courtyard (In the DS version hitting Boos with 8 red coins gives you a secret star), and after 12 stars (15 in the remake) a Big Boo will be in the hallway and also appear in the courtyard. Killing it will result you get access to the fifth level, Big Boo's Haunt. Also in the DS version, there 3 brick blocks, which takes you to The Secret Of Battle Fort course, which is accessible only if you are Mario, Luigi, or Wario, as Yoshi cannot destroy brick blocks. Also one of Luigi's and Wario's rabbits can be found in the courtyard. Luigi's is on the upper alcove (do a backflip spin) and Wario's one is over the fountain, near the two signs.
In Super Mario Odyssey the castle courtyard returns as an Easter egg containing a power star (acting as a Power Moon) after opening several chest in order. The courtyard can be accessed by talking to a Toad behind Peach's castle while wearing the Super Mario 64 costume. The courtyard retains its original design from Super Mario 64.