The Ancient Castle, or Sand Castle is a structure found in the Lost Sands. It serves as the dungeon for Chapter 4. It was created by the Roaches and houses the second half of the Ancient Key. It is filled with puzzles, traps, Roach iconography, and Roach constructs.
According to Venus, it was built when the Roaches still freely roamed around Bugaria.
A depiction of the Everlasting Sapling and the Ancient Artifacts. Its text was too faded to be read.
This ancient mural must've been built by Roaches, given the structure dates back to before Bugaria was established.
Were they seeking it as well, or did they worship it?
Observe the mural on the second floor of the main room.
Leif: This place reeks of ice magic. Vi: I got used to only you being able to do it, Leif! I don't like the cold at all... Kabbu: This is no ordinary castle, evidently. Let's make sure to not be caught off guard once more. Leif: No kidding.
Vi: This is the main room? I thought it'd be more like the Ant Palace! Leif: It doesn't look like a cozy place to live in, for sure. Kabbu: That statue... Is that the Everlasting Sapling? Perhaps this is a place of worship? Leif: It'd make sense if an artifact is here. Vi: It's not a castle without treasure, so let's check every corner!
Sand Pit Room
Kabbu: Goodness. This area is truly enormous! Leif: Because the castle wasn't grandiose enough, apparently. Vi: It's really cold down here, bleh. Kabbu: The sun has never graced this room, it couldn't be helped. Leif: Let's watch our step then. We'd hate to get trapped in yet another basement...
First floor, West Wing
Vi: That's one big ice cube! Leif: It's more of a rectangular cuboid, Vi. Vi: The heck!? Kabbu: It seems quite easy to push... I just wish I could ride it as it sled by!
First floor, East Wing
Leif: We do wonder why the roaches liked building so many statues... Vi: I mean, if I was rich, I'd build a ton of me too! Kabbu: Unrelated to riches, this seems to be more of a cultural matter. Hopefully not greed or arrogance... Vi: Oi...
Rolling Rocks Room
Vi: Eep! D-Don't get squished! Kabbu: This castle has not been very inviting, but this is a tad much! Leif: It's not like we ever feel invited where there's an artifact. Vi: Not the factory's fault you know...
Second Floor, West Wing
Vi: I don't get it. Leif: Thinking's about the only thing that can stop you, huh. Vi: Shut it. Kabbu: Easy now. We cannot just aimlessly press plates. There must be a clue somewhere!
Second Floor, East Wing
Kabbu: This room looks like a storm passed through! We can only wonder what this room's purpose used to be. Vi: We should only wonder how to solve it!
Vi: Ah. Fresh air! Kabbu: We can see all of the desert from here. It's quite soothing... Leif: Maybe we could come back. It's not like anyone owns the place. Vi: This is now my castle! Dibs!
The Watcher's Room (Before Fight)
Vi: Now it's really feeling like a throne room! Kabbu: What are those boxes? I've never seen something like it. Leif: It does give kind of a bad vibe. Stay sharp.
The Watcher's Room (After Fight)
Leif: The rock we found here was quite beautiful. Kabbu: Maybe explorers would mistake it for the artifact? Vi: I sure would have. Glad to have Leif's gibberspeak! Leif: Hmph.
Leif: Our guess is they never expected anyone to make it to this room. Vi: But we did! Team Snakemouth keeps being awesome!
Venus: This castle was built by the Roaches back when they roamed freely around Bugaria. Ah, it still feels like it was yesterday when they were scurrying around the land trying to get stuff together! I tell you, the Sapling brought a lot of blessings but also curses to them... Don't make the same mistake.
This area is similar to the Dry Dry Ruins in Paper Mario. Both castles are in a desert-like area, and require a key to be placed in a hole in an empty room to rise them from the underground. They also have very similar parts, such as corridors with direct views into the desert. Additionally, both areas feature a room with several coffins.