Lab

The  is the workplace and home of the royal scientist, Alphys, in Hotland. It is a single building of technological prowess where Alphys conducts her studies. It also houses the True Lab.

Description
The Lab is a large white and red building with a pale green interior. There are two floors on the lab, the ground floor being Alphys's workplace, and the second floor being her room.

On the ground floor, there is a large screen where Alphys monitors the protagonist, a fridge with a supply of Instant Noodles, a messy desk with her computer, and a "washroom" that leads to the True Lab. Alphys's room is littered with her obsessions and hobbies, including comics, anime figures, an ice cream machine, etc. On this floor, there are unopened letters from many monsters, presumably from the amalgamates' families.

Neutral Route
The Lab is where the protagonist first encounters Alphys after having escaped from Undyne. Here, they are confronted by Mettaton in a quiz show. After deterring him, the protagonist has their Cell Phone upgraded. Then they exit the Lab and proceed on their way towards the CORE.

True Pacifist Route
The protagonist delivers a letter from Undyne to Alphys, who reluctantly opens it and mistakes the protagonist as the writer of the letter. She hangs out with them, Undyne and Papyrus before Papyrus sends her to the Lab and calls the protagonist to recommend they go there as well.

Checking the bin between the computer and screen reveals that someone sent an intimidating message to Alphys, simply saying "I KNOW WHAT YOU DID," written in a strange handwriting. The "washroom" is open and near the doorway is a note from Alphys addressed to her friends, telling them that she needs to face her mistakes and that 'the truth' is past the door. The protagonist enters the door, which is an elevator that takes them to the True Lab.

Genocide Route
The protagonist quickly passes through the Lab, scaring away Mettaton.

If the player aborts their Genocide run at Mettaton NEO, it is implied that when Alphys evacuated the monsters, she brought them to the True Lab. Alphys tells them that she knew she had to do something about the protagonist's actions, even if it meant that the monsters would learn the truth about her.

Trivia

 * In the Windows version of Undertale, the monitor follows the protagonist's movements, whereas the screen displays a static image in Mac OS X version.
 * It is possible to skip the entire scene with Alphys and Mettaton by interacting with the bag of dog food right when the scene begins. This has been dubbed the "Lab Skip" and was first found by a speedrunner named Yozam.
 * In Undertale v1.001, the hitbox of the bag of dog food was shrunk to avoid this from happening. However, this skip is still possible and since Toby Fox could not figure out how to replicate it, it was left in for speedrunners.
 * Interestingly, calling Papyrus's Phone twice in the lab will now cause him to recall seeing Sans with said dog food bag. This may be an ingame reason that explains why the bag's hitbox has shrunk.
 * The bathroom sign and the circuit breaker around the entrance to the True Lab were switched around in Undertale v1.001.