This is the place a character goes to when they're feeling unhappy. Usually, the negative emotion in question is sadness or anger, though it could be fear, only if the fear is very intense (e.g. just hiding from a thunderstorm ain't gonna cut it).
They could be going away to that place for a variety of reasons: maybe their bad mood is making them unwilling to socialise, so they're going to a place where there are little to no people. Maybe they're still trying to avoid people but it's less to do with a desire to avoid socialising and more to do with not wanting to offend anyone. Maybe they're afraid that if they don't take a break, the bad mood might escalate into a complete meltdown. Maybe the place is quiet and they need some quiet to think their bad mood through. Or maybe there's something about the place itself which cheers them up (beautiful view, sentimental value, etc).
To clarify, this is different from being sent to one's room, the naughty step, or to stand in the corner, etc. While these things may be as a result of someone being in a bad mood, it's more of a response to the behaviour the bad mood is causing and is usually more of a punishment than an attempt to cheer the person up. Additionally, characters tend to go to their Bad Mood Retreat voluntarily as opposed to being sent there and some misdeeds that cause a person to be sent somewhere aren't caused by a bad mood at all.
A sign that a character isn't doing too well is if they spend an uncharacteristically long time in their Bad Mood Retreat and/or refuse to leave it, sometimes even to eat, resulting in either forgetting to eat or eating in the place.
Also common are emotional scenes with a character approaching another character who's in their Bad Mood Retreat and having a talk which gets them out of their bad mood (which may be a Rousing Speech, a Pep-Talk Song, a Quit Your Whining speech, a Don't Say Such Stupid Things speech, or even just a simple back-and-forth).
These places may have special names, such as the "Sulking Chair" or the "Sadness Tree". Compare Happy Place and Black Bug Room (which aren't real places), Shower of Angst, Trauma Swing, Bathroom Stall of Angst, Corner of Woe (which can overlap but only if it's one character's special place to go when they're unhappy), and Imagine Spot. If it's a tree or is near a certain plant, it might lead to a Soulful Plant Story.
- Disney Ducks Comic Universe: Scrooge McDuck has a "Worry Room" in his Money Bin. Being the richest duck in the world is apparently very stressful, as the Worry Room is shown to have a circular groove in the floor from Scrooge pacing around in a circle so much.
- Whenever Superman gets overwhelmed by his responsibilities, he retreats to the Fortress of Solitude — an underground complex somewhere in the Arctic that only he can enter because a) only he knows its location and b) only he can lift the colossal key needed to unlock its equally massive entry gate.
- Bloom County. In older strips, when the main cast was feeling bad about world events after watching television, they would go to the meadow and sit in a dandelion patch to feel better. In the strip, this was called a "dandelion break".
- In A Blossom Promise, when Mud the dog is sad because his owner is in the hospital, he lies in his "misery hole".
- The Misunderstood Shark sequel "Friends Don't Eat Friends" involves a shark going to sulk in his "sulking grotto", also known as his "maneater cave".
- Princesses of the Pizza Parlor: The girls' bathroom of the titular pizza parlor is where the girls of the series go, like in the second story, when Katelyn's anger at Claire for events that occurred between games, comes to a head, and she needs a place from everyone else, to calm down.
- In Winnie-the-Pooh, Eeyore has his "gloomy place" where he hangs out a lot of the time. He used to sleep there too, but in "A House is Built at Pooh Corner for Eeyore", he gets his own place.
- Even Moominmama needs one of these - she goes to the ugly grove behind the kitchen. Occasionally used by the rest of the family, too.
- Girl Meets World: Riley and Maya always retreat to Riley's bay window to sort out their emotional baggage with each other, especially if they both have things to be upset over. Because it always gets them to talk and feel better about their problems, they consider it to be some sort of magical spot, a place they can always go when they're feeling down.
- In Sesame Street:
- Alice has two walls she stares at when sad: the "very sad" wall and the "a little bit sad" wall.
- One song features the "Sad Cafe", a place that's allegedly a cafe despite not serving food or drink, where cowboys and cowgirls go to have a good cry.
- Charlie from It's Always Sunny in Philadelphia has his "bad room", an attic room hidden in the labyrinthine air vents of Paddy's Pub. According to Mac, it's where he goes to break bottles when he's upset. Frank accidentally stumbles into it while lost in the vents.
- The Amazing World of Gumball: In "The Stories", Molly hides in an old abandoned restroom, or as she calls it, "her special dark place" whenever she is feeling awkward and lonely. Considering that the entire school shuns her for being too boring, she must be there often.
- Parodied in an episode of Clone High. After an emotional argument, Joan and Abe have a Sad-Times Montage, where they both end up walking to their "thinking docks" at the local pond, so they can stare into the water sadly. Then a different camera angle shows that their docks are right next to each other, five feet apart.
- In the Futurama "Kif Get Knocked Up a Notch", Amy asks if the crew could drop her off to visit Kif while making a delivery nearby. Professor Farnsworth is so offended at her asking that he tells the crew "If anyone needs me, I'll be in the Angry Dome." Shortly after, we do see Farnsworth inside a glass-domed room atop the Planet Express building, ranting to himself and shaking his fists.
- In The Jetsons episode "To Tell the Truth", Jane has a dome to cry in when Elroy breaks her pitcher. Unfortunately, the dome breaks too. By that stage, she's not crying anymore but is still unhappy.
- Downplayed for a tree in Little Princess. The Princess often goes there and climbs up it when she's in a bad mood, but she hangs out there a lot when she's happy too and she doesn't always go there in a bad mood.
- The New Adventures of Winnie the Pooh: In "Donkey for a Day", the others assume this of Eeyore's habit of going off alone to a hill. Subverted when Eeyore finally explains that he comes to the hill when he's happy, enjoys watching the clouds, and is glad to have their company.
- Phineas and Ferb: The Flynn-Fletcher house contains a panic room that has been visited by Candace in the episodes "I, Brobot" when she has a mental breakdown about the Phineas and Ferb robots in their backyard and later in "Invasion of the Ferb-snatchers" when she thinks her brother has been replaced by an alien. She has a teddybear called Mr. Miggins in the panic room to discuss strategies with.