YOU'RE IN MY HOUSE. GOOD CHOICE! THOUGH I GUESS IT'S TECHNICALLY SANS'S HOUSE TOO.
Papyrus when called from inside his 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.
After befriending Undyne, she can be seen in front of this house with Papyrus.
- The date/hangout with Papyrus occurs in his room.
- On the console versions, the Dog Shrine can be accessed by entering through the sink. On the Nintendo Switch version, this is the location where Mad Mew Mew can be fought
- If the protagonist gained no EXP by the time they reach the Last Corridor, Sans's room can be unlocked, and it contains a key to his workshop.
- Papyrus's toolshed is located outside of the house, serving as a makeshift prison if the protagonist loses to Papyrus during his battle.
The first floor of this house contains a living room and a kitchen.
The living room features a television that 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 20 GOLD 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.
The Dog Shrine is an area exclusive to the PlayStation 4, PlayStation Vita, and Nintendo Switch versions of the game that contains a shrine for the Annoying Dog. It is accessible by entering through the sink in the kitchen.
When opening the door of the shrine for the first time, the dog is seen chewing on one of Papyrus's bones and is chased away by Papyrus. Later that moment, Sans's room opens, showing Sans playing his trombone, which annoys Papyrus.
In the PlayStation versions, the protagonist can donate GOLD to the Shrine, 1 GOLD at a time, with 350 GOLD required to fully upgrade it. Upon reaching each donation threshold, a new object is added or the shrine is improved, and the player receives a trophy.
- (2 GOLD) The dog buys some fairy lights.
- (4 GOLD) The dog decides to buy dumplings, which he later dislikes.
- (6 GOLD) The dog buys an inflatable mascot, the kind seen at car dealerships.
- (8 GOLD) The dog steals a picture of Papyrus holding pasta.
- (10 GOLD) A shrine upgrade happens.
- (13 GOLD) The dog buys a radio, which changes the music.
- (16 GOLD) The dog gets a video game.
- (19 GOLD) The dog steals a picture of Papyrus chasing the camera monster.
- (22 GOLD) The dog gets ripped off by rope.
- (25 GOLD) A shrine upgrade happens.
- (30 GOLD) A dog food dispenser is added.
- (35 GOLD) Blueprints are added.
- (40 GOLD) The dog gets ripped off (again) by rope.
- (50 GOLD) The dog tries to get its shrine recognized.
- (70 GOLD) The last dog shrine upgrade.
In the Nintendo Switch version, instead of being able to donate GOLD to upgrade the shrine, the Dog Shrine appears abandoned and destroyed with a door colored red and blue, the colors of the Switch's Joy-Con controllers, in the middle of the north wall of the room. It is sealed with a lock that naturally falls off after defeating Mettaton EX. Interacting with the Mad Mew Mew doll beyond the door initiates the fight.
In the PC version of the game, there are hints in the game files, such as Dog Shrine soundtrack files, that the Dog Shrine was planned to be added.
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 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.
WHY WERE YOU USING A TREADMILL IN THE DARK?
IS SANS PRANKING YOU ACROSS TIME AND SPACE?
I HATE IT WHEN HE DOES THAT!
HOW IMMATURE CAN YOU GET?
Papyrus when he finds the protagonist in Sans’s room
Sans's Room is unlocked in a no EXP earned Neutral 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 notices the protagonist has already heard his spiel and exchanges 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 turns on the lights to the room and tells 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.
HELLO. THAT'S NOT MY HOUSE. THAT'S JUST MY COOL TOOLSHED.
Papyrus discussing his shed
Papyrus's Toolshed, also known as the capture zone, the doghouse, the guest room, the Coolshed, 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 ACCOMMODATIONS 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 gives them the option of skipping the fight, saying that he is getting exhausted from capturing the protagonist. Accepting his offer leads 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 informs 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 reads "WHAT!? THAT'S IMPOSSIBLE."
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.
At the bottom right corner of the room, there is a strange, covered-up machine that seems to be broken. The workshop has four drawers, but the protagonist cannot interact with the rightmost two; in an attempt to do so, they interact with the blueprints on the shelf just above the drawers. The blueprints are described as being of a machine and written in unreadable symbols (which may be the Wingdings associated with W. D. Gaster, or Alphys's handwriting). The second drawer from the left contains a badge. The first drawer's contents change depending on some of the player's previous actions; it always contains a photo album with photos of a happy Sans along with many other people the protagonist does not recognize. After Asriel's battle, another photo shows up with the protagonist, Sans, and all of the protagonist's friends. Finally, only after the v1.001 patch has been applied, and after talking with the Clam Girl and learning of Suzy, a card sticking out from the back flap of the binder appears, described as a poorly drawn picture of three smiling people with the words "don't forget" written in lowercase.
- 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 results in him saying "HOW NICE OF YOU TO CHECK THE MAIL FOR ME. WAIT, NO. THAT'S VERY STRANGE." Checking it again results in him saying "STOP LOOKING INSIDE MY EMPTY MAILBOX. THAT'S MY EMPTINESS, NOT YOURS." Checking it while the protagonist is carrying Undyne's Letter yields different dialogue.
- The Annoying Dog rarely appears 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.
- The Dog Shrine and some of the items that appear in it are likely a reference to a box of items Toby Fox received from fans at a Japanese Undertale event, which he posted about on Twitter. A comment on the post even mentions "two pieces of rope and some blueprints". 
- In the Nintendo Switch version, examining the door leading to Mad Mew Mew in the Dog Shrine before it is unlocked yields a message saying that the door is locked by a mysterious seal, as an ominous piano jingle is heard. This is a likely reference to Chrono Trigger, which has a similar scenario occur when the player tries to open one of the Sealed Chests before a plot-critical event takes place.
- Papyrus's Toolshed has almost the same layout as Napstablook's house.
- (It's hard to read because of the handwriting, but you try your best...) — Flavor text before reading Alphys's note
- (There's a photo album inside the drawer.) (There are photos of... Huh?) (A card is sticking out from the back flap of the binder.) (It's a poorly drawn picture of three smiling people.) (Written on it...) "don't forget." - First drawer, Sans's workshop
- Undertale- Giving Undyne's letter to Papyrus. - YouTube
- Just got back from Japan. There was an UNDERTALE event last weekend and I received a "dog shrine" box of items from fans. Thanks everyone - Twitter
- customs guy at airport: "excuse me sir why do you have two pieces of rope some blueprints in here" - Twitter