Peach's Castle Garden
Mario and Luigi first enter into the gardens after destroying the Dark Star's barrier with the Miracle Cure they formed by the three Star Cures by Doctor Toadley. The players need to find a way inside the castle, but the main doors have been sealed shut. The Blue Paratroopas flying overhead lead the brothers to find a massive attack block in the bottom left corner of the garden. Hitting it as Shell Mario will allow the bros. to gain seven Attack Pieces. This will infuriate the Blue Paratroopas, demanding them to be paid for hitting the block. They first demand that they give him 30 Coins, but later 300 coins for them being so quick to answer yes. As a result of the massive loot, the leader will show Mario and Luigi the last three blocks for the remaining pieces are. They are invisible, so the Bros. have to jump randomly in order to find it. The end result will allow the Bros. to perform the Special Attack, Falling Star.
Once the player has navigated through the garden - over hedges and through tight spots - they will reach a massive trash dump with a fire and a pipe leaking water in the same area. This is the first use of Mario being able to drink tons of water and have Luigi hammer him to eject the water. Doing so puts out the flames, creating a Tornado for the Bros. to Spin Jump their way across. However, even with the small leap ahead, they end up at another pile of junk, where Midbus comes. He attacks the brothers with his trash robot Junker, who has gone out of control after Midbus breaks the controller.
Once the battle between Junker and the brothers is complete, Junker will malfunction again and rampage through some of the trash, as well as tossing the safe that Bowser is in onto a platform that is within the sharp piles of rubble. It will continue rampaging into the next room, and finally fall apart. Mario and Luigi can head into the other room now to find a pink pipe that leads into Bowser's Body and continue the adventure even further. Of course, they need to go to the Lumbar Nook to fix Bowser's Back before they continue on.
Once Bowser is up and moving, as well as knowing how to use the Spike Ball move, he can check the last part of the gardens. Through there, on the other side of Peach statues retouched with Fawful features, is a little tower that Bowser can enter into. All Bowser has to do is crumble the statues into bits with his newly learned move and crawl up the soft portion of the tower's wall to enter the castle.
Here is a list of overworld items found in Peach's Castle Garden during the events of Mario & Luigi: Bowser's Inside Story.