Papyrus and Sans's House

Papyrus and Sans's House is a location in Snowdin. Christmas decorations adorn the house, and it is unlocked after the protagonist befriends Papyrus. 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 outside with Papyrus in front of this house after the protagonist befriends her.

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 when turned on. The living room also hosts Sans's pet rock, which is covered in sprinkles, and one of Sans's dirty socks with a series of sticky notes attached to it. These sticky notes depict Papyrus nagging Sans to pick it up. The living room also contains 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. The protagonist decides to stop 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 labeled "spaghetti" on one side and an empty bag of chips on the other.

Second Floor
The second floor of the 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 reading (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 clothes neatly hung up inside.

Sans's Room
Sans's Room is unlocked in the True Pacifist Route by listening to Sans in the Last Corridor explain EXP and LOVE and then reloading the SAVE file. This can also be accomplished by having already completed the Neutral Route once and then returning to the area in a second Neutral Route. After either method, Sans will notice the protagonist has already heard his spiel and exchange one codeword, and then another, which is revealed by reloading again. Sans then gives the protagonist the key to his room, which mysteriously appears on the protagonist's keychain.

When the protagonist first enters the room, they walk into what is seemingly an empty void. After a bit of walking, Papyrus will turn on the lights to the room and tell the protagonist that they were using a treadmill in the dark.

Sans's room is messy, containing a self-sustaining tornado of trash, an unused treadmill with a note that reads "the truth is that you got owned, nerd....." It also contains 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 is out of batteries stuck in the bulb socket, and a drawer with a Silver Key, clothes, and trombones inside of it.

Papyrus's Toolshed
Papyrus's Toolshed, 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 Papyrus and Sans's House. 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 is 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 is getting exhausted from 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 attempts to access the shed after befriending Undyne, Papyrus will inform the protagonist that it is his " COOL TOOLSHED. ". Undyne then exclaims "Do you call it your coolshed!?" Papyrus admits that he has never thought of that, and adds " THAT'S WHY WE'RE FRIENDS, UNDYNE. YOU ENRICH MY LIFE WITH SHED-BASED PUNS. " Undyne comments that this is the only shed-based pun that she has ever made.

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, with two being inaccessible. One drawer contains 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 many people the protagonist does not 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. After talking with the Clam Girl, 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.
 * 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" . Checking it while the protagonist is carrying Undyne's Letter will yield different dialogue.
 * The Annoying Dog will rarely appear in the self-sustaining tornado of trash in Sans's Room.
 * There is a bug that occurs when the protagonist looks under the sink. The Annoying Dog's tail clips through the right side of the sink when its eyes widen upon being found.