Underground laboratory

The  is Stan Pines' secret hidden room under the Mystery Shack, the entrance to which is hidden behind a vending machine in the gift shop. Stan secretly entering the room behind the vending machine is briefly shown in "Tourist Trapped" and "Dreamscaperers." The inside of the room is finally presented in the season 1 finale, "Gideon Rises."

History
In "Tourist Trapped," Stan is shown mysteriously entering a room behind a vending machine, marking the end of the episode. The room wasn't seen or mentioned in the following episodes until "Dreamscaperers." Bill Cipher (disguised as Soos) opens a "memory door" in Stan's mindscape where he finds Stan entering behind the vending machine saying "If only people knew the truth, that hidden behind this vending machine I secretly have a...". Bill gets bored and closes the door before Stan finishes his sentence. The inside of the room is finally revealed in "Gideon Rises," where Stan has collected all of the journals (1, 2, and 3). He then enters codes from them to activate a portal-like device which activates, to Stan's grim pleasure.

Appearance
In order to get inside the laboratory, Stan has to go through a series of security measures. First he unlocks the vending machine code, goes down a set of stairs behind it, opens a panel beside the elevator and inputs the alchemical symbols for "composition," "pulverize," "digestion," and "fusion," followed by the 'down' button. He then gets inside the elevator and rides it to the third floor.

The laboratory room is filled with retro futuristic looking computers, gadgets, and machines, all of them constantly working. At the end of the room is a desk with many electronic devices and on the side it has the symbol of Stan's tattoo. On the desk there is a picture of Dipper and Mabel, and in the shelf below a series of books in which Stan hides the journal number 1. Near the desk there is a door entering into a room consisting of a triangle shaped device with a circle inside that has 16 symbols.

Surveillance center
When Stan enters the lab, he walks by the base of the Totem pole which is located outside of the Shack, if looked at closely, a periscope is seen inside the pole. Even more so, a surveillance screen is seen on the bottom with an image of trees from somewhere outside of the Mystery Shack.

During "Scary-oke", the surveillance screen showed Dipper and Mabel on the run from zombies, but Stan was too focused on his work with the portal to notice.