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The Underground is a shop in Palia accessible at night from 6:00 PM to 3:00 AM. It's run by the villager Zeki, and features a static register shop, a rotating selection of furniture and decor not craftable in each set in Furniture Making, access to The Tower, and Zeki's Wondrous Machine. Players can play the Hotpot Minigame here as well!
Each night in Palia there is a small rotating stock of furniture and decor available for purchase with Gold in Zeki's Grimalkin Underground. These include furniture infused with Flow like plumbing and electronics, rugs, and paintings.
Here is a list of all possible items with their Underground prices:
Hotpot is a minigame that can be played to earn Gold. To play, interact with any open hotpot table in the underground during the Underground Market hours (6:00 PM to 3:00AM Palian Time). Up to four different Players can play at each hotpot table.