Peach's Castle is the main location of SuperMarioGlitchy4's bloopers. It is the official residence of the monarch of the Mushroom Kingdom, and the primary residence of Princess Peach. It has been present in a majority of bloopers and games, and is especially used in older videos.
Peach's Castle takes on the form of its Super Mario 64 variation. The exterior is made of grey bricks, with four towers at each corner. At the front of the castle is a bridge leading to the double doors to enter the castle. Above them is a stained glass window of Princess Peach. In the center of the castle is a large, two-tiered tower. The castle is roofed with red shingles. Many windows also appear on various walls in the castle.
The interior of the castle has light, cream walls. The flooring consists of both checkerboard tile and red carpet, the latter being used for most stairs, pathways, and side-rooms. The doors to the individual rooms are made of dark-brown wood.
While he does have his own house, as shown in many cases, Mario is more commonly seen at the castle. Mario even eats and sleeps at the castle, as shown on numerous occasions. The most likely reason for Mario's common overnight stay is laziness, as he may just not want to go back home.
While not as commonly seen as his brother, Luigi is also a common resident of the castle. Luigi likely stays at the house when not at the castle and when Mario is adventuring, usually spending his time drinking tea, as stated in Meet the Luigi.
Toad may be the most commonly seen character in the entire castle, as he usually appears in the corner in the main room. He doesn't move very much from that specific spot, so Toad is usually caught up in the shenanigans that occur in the castle.
He has attempted to leave the castle many, many times, but he has been thwarted by Mario each time.
As he does not seem to have any other residence in the bloopers, SMG4 is the main resident of the castle. SMG4 usually spends most of his time cooped up in the right room after the stairs, as his desktop and editing equipment are commonly shown in that room. Other objects also appear in this room, most commonly a toilet.
Presumably, he was responsible for setting up a defense system that they could use to defend themselves from the Teletubbies during the Purge.
While not staying for long periods of time, Steve commonly castle-crashes at seemingly random occasions, soon following with his signature "Hi guys!" line.
Fishy Boopkins sometimes pays the castle a visit. During Mario and the T-Pose Virus, he was seen playing cards with Meggy and Bob.
Sometimes, Meggy pays the castle a visit. There is a secret sewer tunnel that connects the castle to Inkopolis.
Bowser's UsurpingBowser, during the events of The Adventures of Mario and Luigi - Ep. 2 and Episode 3, temporarily usurped the castle and turned it into a second Bowser's Castle for him to reign in. The usurped castle would receive a massive appearance change from it's original state. The ground becoming a military green with green "spinny shy guys" standing guard and torches at the shoreline.
The castle itself uses dark shades of grey along with windows with black outlines and orange insides. The castle's glass pane showing Princess Peach has also been replaced with a giant Bowser crest that apparently allows Bowser to broadcast on it in order to taunt the brothers. Bowser's usurping of the castle lasted until The Adventures of Mario and Luigi - Ep. 3 with the castle and it's grounds presumably being fixed sometime before The Adventures of Mario and Luigi - Ep. 4.
Grand Dad's Usurping
When Mario lets Grand Dad out of the bootleg dimension in SM64: THE BOOTLEG DIMENSION, he turns a bunch of characters and the castle into a ton of bootlegs and a glitchy design respectively but Mario turns it back.
Toad decided to blow it up when he became the president of the Mushroom Kingdom.