- Papyrus and Sans are the first characters to make their debut, and they host many of the puzzles the protagonist encounters.
- The Mysterious Door can be found in this region, along with a hidden enemy called Glyde.
- The "Snowdin Canine Unit" resides here, making this region the most concentrated area of Royal Guard members in the Underground.
- The protagonist can find the Tough Glove in a box and can purchase the Manly Bandanna from the Snowdin Shopkeeper.
- The final enemy of this region is Greater Dog. After passing them, the protagonist encounters Papyrus and Sans for the last time before reaching Snowdin Town.
After confronting Toriel and leaving the Ruins, the protagonist meets Sans and Papyrus in Snowdin Forest. Sans jokes with them, and Papyrus attempts to jape them with puzzles. The protagonist encounters the members of the Snowdin Canine Unit of the Royal Guard as they make their way to Snowdin Town. They can also accept a snowman's offer to take a Snowman Piece with them on their journey. The protagonist is Nice Cream Guy's first customer, and they give him hope for his business. Once the protagonist passes the Gauntlet of Deadly Terror, they enter Snowdin Town.
During his initial encounter, Sans notices the protagonist's lack of reaction to his joke. The protagonist also walks through Papyrus's puzzles, to his dismay. Sans attempts to redirect the protagonist, but eventually threatens them and warns them of what will happen if they continue the Genocide Route.
Coniferous trees, snowfields, and small cave systems populate Snowdin Forest, and this region has many characteristics of a taiga biome. It also includes a large river that flows east; Ice Wolf uses this river to transport ice to the CORE. Snow blankets the ground throughout Snowdin Forest and Snowdin Town.
Ruins Exit and Box Road
The first room of Snowdin Forest is long and horizontal, and coniferous trees provide a constant background. As the protagonist walks to the right, coniferous trees freckle the foreground, allowing Sans to appear as a silhouette between them as he follows the protagonist. A sturdy branch blocks a part of the path and, as the protagonist passes by it, the branch splinters. After his introduction, Sans informs the protagonist that his brother constructed the wooden bridge. After crossing the bridge, the protagonist hides behind a conveniently-shaped lamp, which is located next to Sans's sentry station and a couple rocks. This area serves as Papyrus’s first appearance as the brothers talk to one another.
The right end of the first room connects to the "Box Road", which has a SAVE Point and a box that contains the Tough Glove. The north exit of this room connects to the river with a fishing rod holding a note underwater. The right exit leads to the next encounter with Sans and the protagonist’s first encounter with Papyrus.
Box Road to Spaghetti Trap
The horizontal room that features the encounter with Sans and Papyrus also houses Papyrus's cardboard sentry station near the east exit. This exit leads to a short horizontal room that contains Doggo's sentry station and the first canine mini-boss battle, in which Doggo introduces blue attacks. There are dog treats to the right of Doggo's station.
After going through the east exit, the protagonist encounters Sans and a patch of ice that they can slide on. A sign in the middle of the ice reads that ice is in all directions and that Snowdin Town is to the east.
To the north of the ice room, a snowman offers the protagonist a piece of himself to take with them on their travels. The east exit of the ice room leads to the Invisible Electricity Maze, hosted by Sans and Papyrus. This small room connects to a larger room that has the Nice Cream Guy, who sells Nice Cream, the snowdecahedron, as well as the Ball Game. The exit in the top right of this room leads to the sentry stations of Dogamy and Dogaressa, and also includes a sign that explains "smell danger ratings."
The bottom right exit of the large room leads to another encounter with Sans and Papyrus. A word search lies on the ground, provided by Sans. The east exit of this small room leads to the "Spaghetti" room, which contains a SAVE Point, a note from Papyrus, frozen spaghetti that is stuck to the table it is on, and a microwave. The microwave and spaghetti are on separate tables. A wall to the north has a mouse hole and, atop this ledge, there appears to be frozen flowers.
Spaghetti Trap to Dog Sculptures
The east exit of the "Spaghetti" room leads to a large room whose exit is blocked by spikes. At the bottom left of the room, there is a map covered in snow that the protagonist can reveal by walking over it. The switch to retract the spikes is located between two coniferous trees in the upper right of the room.
After passing the retracted spikes, the protagonist encounters the Dogi. Once the Dogi are defeated, the protagonist can leave the large room through the south exit and complete the first XOXO puzzle. Once completed, spikes near the east exit of the room retract, and Papyrus questions the protagonist about the state of his spaghetti trap.
After leaving through the east exit, the protagonist encounters the second XOXO puzzle that Papyrus supervises because he modified the puzzle while he was waiting. Again, spikes prevent the protagonist from leaving the room through the east exit until they complete the puzzle.
The next room hosts the first instance of the Multicolor Tile Puzzle, which has a console that looks strikingly similar to Mettaton. Both Sans and Papyrus look on as the machine creates a simple "puzzle" for the protagonist to solve; Papyrus spins out of the room without saying a word.
If the protagonist asks Papyrus to repeat the rules for the Multicolor Tile Puzzle multiple times, he becomes confused and tells the protagonist to try the puzzle on their own. Papyrus leaves illegible instructions and walks offscreen.
Leaving the Tile Puzzle room through the east exit leads to the "Dog House" room, which contains Lesser Dog's station and, depending on the protagonist's actions during Lesser Dog's encounter, various degrees of snow sculptures. If the protagonist killed Lesser Dog, the statues are replaced with a pile of mushy snow.
Dog Sculptures to Snowdin Town
The east exit of this room leads to the third and final XOXO puzzle, which the protagonist has to slide on ice to solve. Falling off of the edge of this puzzle causes the protagonist to leave this room and appear in a room directly south of the XOXO puzzle. This room contains a snow Papyrus and a lump of snow with Sans's name written on it. The north exit of this room leads back to the XOXO puzzle.
A bridge that leads to the east exit of the room forms after the protagonist completes the puzzle, and they can slide through a tunnel of coniferous trees to get to the next area. Directly south of the bridge is an area where the protagonist encounters Gyftrot and where the Mysterious Door is located.
Within the small room that contains the Mysterious Door, two lantern mushrooms can be turned on and off with no consequence. Within this small room, the protagonist can encounter a hidden enemy, Glyde.
Backtracking to the ice bridge's exit, if the protagonist travels east, they encounter a room full of snow poffs. If every snow poff is inspected and interacted with, the protagonist receives 30G. This room also contains the small doghouse of Greater Dog. Near the east exit, Greater Dog's encounter with the protagonist occurs after they rise out of the snow disguised as a snow poff.
After defeating Greater Dog, the protagonist can leave the room through the east exit and approach the last puzzle, The Gauntlet of Deadly Terror. Papyrus threatens to activate the Gauntlet but ultimately decides not to.
After crossing over the long bridge, the protagonist leaves Snowdin Forest and enters Snowdin Town.
The forest section overseen in the background by the bridge is inaccessible to the protagonist.
- In the area right outside the Mysterious Door, there is a tiny house seen from the cliff. If the protagonist waits, a person leaves and re-enters the house.
- Several of Alphys's cameras can be found throughout this region. In Snowdin Forest, their locations include:
- The bush directly outside the Ruins.
- The trees behind Sans's sentry station.
- The tree behind Papyrus's sentry station.
- The lump of snow to the left of the snowdecahedron.
- The tree next to the "dog marriage" sign.
- The tree behind the sentry station near Lesser Dog's snow sculptures.
- At both ends of the Gauntlet of Deadly Terror.
- If the protagonist calls Papyrus on the long bridge, he states that the bridge is just a rock formation that he painted over.
- The sign by Dogamy and Dogaressa's sentry stations describes humans with the threat color of GREEN, the word "GREEN" highlighted in red. This references the condition of red-green color blindness in dogs.
- When passing through trees in Snowdin Forest, four possible shapes can form on the protagonist's head: a house, a bird, a hat or a dog.
- If the protagonist returns to Snowdin after Undyne's battle, they can meet the teens mentioned by Gyftrot, and the teens tell the protagonist more about Snowdrake's story.
- If the game's FUN value is set to a certain value, the protagonist may receive one of two phone calls in the room with Papyrus's sentry station:
- If the FUN value is between 40-45, Sans calls to ask if the refrigerator is running. Answering yes causes him to say that he will "be over to deposit the brewskis." Answering no causes him to say that he will send someone over to fix it.
- If the FUN value is between 46-50, Alphys calls to order pizza and attempts to send the requested toppings via text. However, what she actually sends over is ASCII art of an anime catgirl, which the protagonist's cell phone, being too old to receive texts, reads out loud, character by character.
- If the protagonist interacts with the snowdecahedron on the Genocide Route or after exhausting the kill counter on the Neutral Route, the message "It's a snowball." displays instead.
- "I want to see the world... But I cannot move. If you would be so kind, traveller, please... Take a piece of me and bring it very far away." – Snowman
- "OH!!!! A CUSTOMER!!!" – Nice Cream Guy
- "that's, uh. your cue to laugh. or, uh, to emote at all...?" – Sans
- "...ARE YOU SERIOUS? SANS!!! HELP!!! THEY KEEP WALKING THROUGH MY PUZZLES! THEY'RE SUPPOSED TO LET ME EXPLAIN THEM. THEN THREATEN AND BAFFLE THEM WITH DANGEROUS JAPES" - Papyrus
- "hey... puzzles might be fun. if you tried them." – Sans
- "say, i've been thinking. seems like you're gonna fight my brother pretty soon. here's some friendly advice. if you keep going the way you are now... you're gonna have a bad time." – Sans
- "(It's been smashed like it was nothing...)" – Flavor Text
- "i have an idea. go through this gate thingy. yeah, go right through. my bro made the bars too wide to stop anyone." – Sans
- "It's some sort of checkpoint or sentry-station. But there are bottles of ketchup, mustard, and relish sitting inside..." – Flavor Text
- "YOU OBSERVE THE WELL-CRAFTED SENTRY STATION. WHO COULD HAVE BUILT THIS, YOU PONDER... I BET IT WAS THAT VERY FAMOUS ROYAL GUARDSMAN!" – Note on cardboard box
- "SMELL DANGER RATING
Snow Smell – Snowman
Can become YELLOW Rating.
Unsuspicious Smell – Puppy
Smell of rolling around.
Weird Smell – Humans
Destroy at all costs!"
– Sign between Dogamy and Dogaressa's sentry stations
- "THE NEXT PUZZLE WILL NOT BE EASY! IT IS DESIGNED BY MY BROTHER, SANS!" – Papyrus
- "(YOU'LL BE SO BUSY EATING IT...) (THAT YOU WON'T REALIZE THAT YOU AREN'T PROGRESSING!!) (THOROUGHLY JAPED AGAIN BY THE GREAT PAPYRUS!!!)" – Papyrus's note
- "(It's a plate of frozen spaghetti.) (It's so cold, it's stuck to the table...)" - Flavor Text
- "IS THERE ANY LEFT FOR ME???" – Papyrus
- "HMMM... HOW DO I SAY THIS... YOU WERE TAKING A LONG TIME TO ARRIVE, SO... I DECIDED TO IMPROVE THIS PUZZLE... BY ARRANGING THE SNOW TO LOOK MORE LIKE MY FACE. UNFORTUNATELY, THE SNOW FROZE TO THE GROUND. NOW THE SOLUTION IS DIFFERENT!" – Papyrus
- "It's illegible chicken scratch." – Flavor Text
- "MAYBE... TOO EASY TO DEFEAT THE HUMAN WITH. YEAH! WE CAN'T USE THIS ONE!!! I AM A SKELETON WITH STANDARDS!!! MY PUZZLES ARE VERY FAIR! AND MY TRAPS ARE EXPERTLY COOKED! BUT THIS METHOD IS TOO DIRECT! NO CLASS AT ALL! AWAY IT GOES!" – Papyrus
- "I THINK IT LOOKS MORE DRAMATIC THAT WAY. I ADDED THE ROPE, TOO." – Papyrus
- Undertale - List of "fun" and "Fun" Events (0:43)
- Undertale - List of "fun" and "Fun" Events (1:09)