Papyrus and Sans's House

 is located in Snowdin. The house is decorated with Christmas decorations and is unlocked when Papyrus has been befriended. To the left of the house is Sans's mailbox, which is full of junk mail, and Papyrus's empty mailbox.

Undyne can later be seen hanging out with Papyrus in front of this house after befriending her in the Pacifist Route.

First Floor
The first floor of this house contains a living room and a kitchen.

The living room features a television which is always set to one of Mettaton's shows, Sans's pet rock covered with sprinkles, a dirty sock that belongs to Sans with a series of sticky notes next to it which depict Papyrus nagging Sans to pick it up, an old couch that gives the protagonist loose change when they first check it, and a joke book that contains a quantum physics book which contains another joke book containing another quantum physics book; but the protagonist stops at this point.

The kitchen contains a stove with an empty pie tin in it, a trash can, a tall sink, and a fridge that has containers labelled "spaghetti" on one side and nothing but an empty bag of chips on the other.

Second Floor
The second floor of this house contains a framed painting of a cartoon bone and doors leading to Papyrus's room and Sans's room. The door to Papyrus's room is plastered with labels saying (NO GIRLS ALLOWED!), (NO BOYS ALLOWED!)  and (PAPYRUS ALLOWED.)  The door to Sans's room has multicolored flames under the door which do not hurt the protagonist if stepped on.

Papyrus's Room
Papyrus's Room is where the protagonist befriends Papyrus.

His room contains a racecar bed, action figures, pirate flag, a bookshelf with complex tomes about puzzle creation and children's books, a computer opened up to a social media website, a box of bones, and a closet with neatly hung up clothes.

Sans's Room
Sans's Room is unlocked in the Pacifist Route by listening to Sans in the Final Corridor explain EXP and LOVE and then repeatedly reloading the SAVE file. After the third reload, Sans will notice the protagonist has already heard his spiel and exchange two codewords. Once this is accomplished, Sans will give the protagonist the key to his room.

When the protagonist first enters the room, they walk into what seemingly is an empty void. Papyrus then turns on the lights to the room to tell the protagonist that they were using a treadmill in the dark.

Sans's room is generally messy with a self-sustaining tornado of trash, an unused treadmill with a note that reads "the truth is that you got owned, nerd.....", a dirty sock pile, a worn mattress with sheets bundled up in a weird creasy ball, an uncovered pillow, a thank you letter addressed to Santa, a lamp with a flashlight that's out of batteries stuck in the bulb socket, and a drawer with a Silver Key, clothes, and trombones inside of it.

Papyrus's Shed
Papyrus's Shed, also known as the capture zone, the doghouse, the guest room, or Papyrus and Sans's garage, is a small shed located to the right of. It is where the protagonist gets trapped in when they manage to lose and get captured by Papyrus. The conditions in the shed are changed slightly every time the protagonist loses to Papyrus.

The shed starts out with a bowl of dry food, a squeaky chew toy, and a bed that's too small to sleep on. There is a note that reads '' "SORRY, I HAVE TO LOCK YOU IN THE GUEST BEDROOM UNTIL UNDYNE ARRIVES. FEEL FREE TO MAKE YOURSELF AT HOME!!! REFRESHMENTS AND ACCOMIDATIONS HAVE BEEN PROVIDED. -NYEHFULLY YOURS, PAPYRUS." '' The bars of the shed are built too far apart, just like the ones on the bridge in Snowdin Forest, so the protagonist can easily escape from it.

The second time the protagonist loses, there is a hot dog cut up into the bowl of kibble and the note has been changed, now reading: '' "PLEASE ASK BEFORE YOU ESCAPE!!! WHEN YOU WENT MISSING I GOT WORRIED SICK!!! -SLIGHTLY BONETROUSLED, PAPYRUS."  The third time the protagonist loses, Papyrus's note just says:  "IF YOU'RE JUST LOOKING FOR A PLACE TO STAY... JUST ASK!!! YOU DON'T NEED TO FIGHT ME!!! -YOUR HOST, PAPYRUS." '' The word "Bonetrousled" in the second note is likely a reference to the track that plays while fighting Papyrus, Bonetrousle.

After three losses to Papyrus, the next time the protagonist meets him, he will give them the option of skipping the fight, saying that he's getting really tired of capturing the protagonist. Accepting his offer will lead to the same post-fight dialogue as if the protagonist had fought and spared him normally.

If the protagonist accesses this room via messing with the save data, the note will read '' "WHAT!? THAT'S IMPOSSIBLE." ''

Sans's Workshop
Sans's Workshop is located in the house's basement. It can be found behind the house and can only be opened with the Silver Key found in Sans's room.

The workshop has four drawers. Two of them contain blueprints of a machine written in strange symbols which are believed to be wingdings. The next drawer contains a badge, and the last drawer contains an album with Sans and a lot of people the protagonist doesn't recognize. If the game has previously been completed with any ending, another photo will show up with the protagonist, Sans, and all the protagonist's friends. There is also a card with a poorly drawn picture of three smiling people with the words "don't forget". A patch to the game changed this text slightly. At the bottom right corner of the room, there is a strange covered up machine which seems to be broken.

Trivia

 * The garbage bag inside the trash can that the protagonist is free to visit anytime is named "Trashy".
 * No music plays in Papyrus's Room while in the overworld, even during the True Pacifist Ending epilogue where "Reunited" plays in every other room.
 * Although there is a visible balcony on the right side of the house, it appears it cannot be accessed.
 * When the protagonist visits Papyrus's house for the first time, right before the date/hangout, continuously walking in and out of Papyrus's kitchen at a rapid pace causes him to dash quickly to the left and right (as Papyrus follows the protagonist to the kitchen when they enter it, then goes back to where he originally was as they exit it). Eventually, a tinkling sound will be heard every time the protagonist switches rooms, leading to a different 'completion' sound. If the protagonist talks to Papyrus after the completion noise, he'll mention he can't feel his legs, which must mean he is a great host; if they stop before that, he'll instead say that being a great host is a good workout.
 * Checking Papyrus's mailbox with him next to it will result in him saying  "THANK YOU FOR CHECKING MY MAILBOX FOR ME... NO WAIT, THAT'S WEIRD." . Checking it again will result in him saying  "STOP LOOKING IN MY EMPTY MAILBOX, THAT'S MY EMPTINESS, NOT YOURS" .