The party's hangar-sized level-five conjoined personal space, complete with training room, crafting studio, and Mordecai's quarters.
The Royal Palace is the party's personal space, unlocked when Carl, Princess Donut, and Katia Grim pool AI-gifted coupons and Mordecai conjoins three level-three spaces into a single level-five communal hall. Cavernous as an airplane hangar, it holds individual bedrooms, a shared kitchen and living area, an Enhanced Crafting Studio, a Training Room, an ultra-stabilized bed granting full rest in two hours, and — for the first time — Mordecai's own attached manager's quarters, freeing him from random teleportation. It becomes the base from which the party trains, crafts, and plans their assault on the rails.
An industrial airplane-hangar-sized concrete space with a very high ceiling, customizable glowing doorways, and modular rooms (bedrooms, kitchen, living area, crafting studio, training room) slotted into the open floor.
The party's home base and crafting/training hub on the fourth floor.
Also appears in books you've already read — spoiler-safe to their endings: