Card Castle is the final area of the Dark World in Chapter 1 of Deltarune. It is the home of King and Lancer and is guarded by some variant of every Darkner encountered up to that point. The Knight used the location of Card Castle for the Eastern Fountain.
Located in the basement of Card Castle, 1B contains the prison cells which the party is thrown in upon reaching the castle. There are two puzzles in the prison area. Inside the prison cell, Kris can acquire the Iron Shackle and eat moss in the corner, restoring all of their health. Ralsei has additional dialogue once both actions are taken.
South of the prison cells in which the party is locked up, a Pair of Eyes is locked up to the left. To the right, several circus cages hold the three former kings who were imprisoned after the Knight arrived, a Jigsawry who made an illegal puzzle, a Rudinn who didn't want to fight and a group of circus animals who have to live in one cage now that the others are occupied. A long elevator ride takes the party up to 1F.
After King is overthrown by Lancer, he is locked away in the prison cells located on this floor.
The palace gate is located to the south on this floor. The elevator to Prison 1B and the "??????" floor is at the lower right, while the elevator to 5F, which is stuck at the top until the first time the party rides it back down, is at the upper right. The stairs to the next floor up are at the upper left.
1F is associated with the Diamond suit. One of its corridors is guarded by Rudinn Rangers. To the lower left, a diamond-shaped door leads to Rudinn's Room. If the party previously violently defeated Rudinns, one of the Rudinns inside can be apologized to. The Rudinn accepts the apology, altering the chapter's ending if no other types of enemies were violently defeated.
This floor is not associated with a card suit, and is instead inhabited by four Whip Ponmen which must be avoided to reach its safe corridors. The stairwell down to 1F is to the left, and the one to the next floor is to the north. At the far right, the party first encounters Rouxls Kaard, whose puzzle they must solve before proceeding. At the lower left, a treasure chest holds a Clubs Sandwich. At the lower right, a bathroom, the Royal Flush, is occupied.
3F is associated with the Hearts suit. The stairwell down is located at its top center, from which each egress is guarded by Head Hathys.
To the right, a room with a heart-shaped doorway holds four beds and two Hathys. If Kris inspects each bed, their title changes from LV1 Leader to LV1 Bed Inspector. If the party violently defeated two or fewer Hathys, interacting with the Hathy on the right causes Ralsei to apologize and the Hathy to forgive the party, altering the chapter's ending if no other types of enemies were violently defeated.
A stairwell up to 4F is located to the left.
4F is associated with the Clubs suit. The floor's upper area is guarded by Scissor Dancers. The stairwell down is in the far left corridor. Rouxls Kaard appears again in the far right corridor, with a puzzle which must be solved before the party can proceed.
After solving the puzzle, the southern corridor opens up. At the lower left, a club-shaped door leads to a birthday party being thrown for Clover, attended by Clover, a Hathy, and a Rudinn. A treasure chest near the door contains a Revive Mint. The chest appears once Kris interacts with all of the Lancer portraits on the walls. At the lower right, a stairwell leads up.
The fifth and final floor of Card Castle, 5F contains the game's final save point and access to the roof where the party confronts King.
Floor 5F contains three levels, accessed by two sets of stairs. The first features a general room with Lancer's bedroom, Rouxls Kaard's shop, and an elevator to floor 1F, which can be used to travel from 1F back to 5F after its first time used. On the second level, Rouxls Kaard forces the party to fight a King Round augmented with a "Control Crown." On the third level, a spade-shaped throne sits in a battered throne room which contains the game's final save point. North of the throne room, the party continues ahead for the final confrontation with King.
Jevil can be found on this floor. This location is accessed via the elevator running between Prison 1B and Floor 1F.
- If Kris eats the moss on the prison floor, Susie mentions how they didn't save any for her when brought into the cell.
- According to the elevator sign on floor 1F, the Prison floor was formerly known as "Basement, Which Just Happened to Have A Lot Of Cages" implying the location was not originally a prison floor.
- On Floor 2F, a bathroom door is labeled "Royal Flush," a play on the hand in Poker, as well as on the royal status of Lancer and the King.
- After the solo battle with Lancer, interacting with the area where the metal bars used to be in the prison brings up the message "(There's a conspicuous absence of a metal door here.)"
- When interacting with the leftmost hole in Lancer's room, "(You found 20 Rupys in the hole! Unfortunately, that's not a useful currency around here...)" appears, as a possible reference to Rupees from The Legend of Zelda series.