Card Castle is the final area of the Card Kingdom 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, B1 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 HP. Ralsei has additional dialogue for both actions.
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, a group of circus animals who have to live in one cage now that the others are occupied, and Starwalker if they are talked with in the Forest beforehand. 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 B1 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 chapter'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 subsequently be used to travel between 1F and 5F. On the second level, Rouxls Kaard forces the party to fight King Round - this time augmented with a "Control Crown." On the third level, a spade-shaped throne sits in a battered throne room which contains the chapter's final save point. North of the throne room, the party continues ahead for the final confrontation with King.
This area consists of a long staircase that descends to Jevil's prison. It can be accessed from Floor 1F's east elevator. His door can only be opened with a Door Key, though it was split into Broken Keys A, B, and C.
Upon Jevil's defeat, the party is forced out of his cell, and the cell itself vanishes. The Circus no longer plays on this floor.
- While the player is unable to select Susie's actions versus Lancer, the SOUL can be moved to dodge attacks. The SOUL appears and returns from the top right of the screen during his turn, where Kris and the SOUL is located. Toby Fox has confirmed that this is intentional.
- Returning to Kris and Ralsei's cell and checking where the bars were prompts a narration. "(There's a conspicuous absence of a metal door here.)"
- 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 east elevator sign on Floor 1F, the Prison was not originally a prison floor.
- When the east elevator reaches ??????, the outline color of the elevator room changes from white to a faded dark blue.
- On Floor 2F, a bathroom door is labeled "Royal Flush." It is a play on the hand in Poker, as well as on the royal status of Lancer and the King.
- 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.
- UNDERTALE 6th Anniversary So We Play DELTARUNE Chapter 1 For Some Reason - LIVE! - YouTube
- (Formerly known as Elevator to Basement, Which Just Happened to Have A Lot Of Cages.) - Narration for east elevator sign on Floor 1F.