Sauna of Death

The Hero is trapped in a sauna or steam room by some villain who has locked/barred the door and must get out before dying of dehydration/heat-stroke.

This trope amuses people who are used to real saunas to no end: in any real sauna, because of the tendency of heat to rise up, one can easily lie down on the floor, which tends to remain cool even in the hottest saunas. This might work in a Roman sauna, which uses hypocaustum (underfloor heating) to heat the bath. The Romans used wooden clogs called coturnae to avoid their feet getting burnt.

Similar in ease-of-escape terms but opposite in temperature terms to Locked in a Freezer. Occasionally, when characters of opposite genders are featured, they will be driven to strip off at least the outer layers of their clothing. This generally has an effect similar to the freezer situation in which the characters huddle together for body warmth.

May be used as an example of Homicide Machines.

May be an Amusing Injury in Cartoons if the character physically shrinks in size, like a piece of laundry, or becomes skeletally thin from too long in a steam cabinet.

Examples of Sauna of Death include:

Anime & Manga

Subverted in Gintama, where somebody tries to do this to Gintoki and Hijikata... only instead of realizing the villain is there, they just accept it as part of a challenge and start trying to make things even hotter. Unsurprisingly, this episode drew waves of squealing fangirls.
The bizarre Widget Series Kiki Ippatsu Musume uses this as one of the many life-and-death situations in which protagonist Kunyan finds herself. Keeping with the series' Finagle's Law setup, the door isn't locked but she can't open it because both her arms and legs dislocated simultaneously. When she tries to open the door with her mouth, the first attempt bashes her nose against the door and the subsequent nosebleed makes the knob slippery and harder to turn. Yeah, it's that kind of series.
Was once attempted on Lupin III by an enemy (A safemaker's son seeking revenge). In this case, it was one of those enclosed one-person units. Lupin, of course, managed to escape and the kid was expecting as much. The sauna was a warning shot. (His ultimate plan was: Poison Lupin and cuff him to Fujiko to force Lupin to try and crack a super-safe containing the key and antidote and then admit defeat to restore the safemaker's reputation).

Comic Books

In an Archie comic book, Veronica was placed in an overheating steam cabinet and left to die by a supervillain. Jughead (who was in superhero mode) was charged with rescuing her, but didn't do a very good job of it. Losing quite a bit of weight and starving the ordeal, she consumed a vile concoction the beanied one had prepared earlier for his lunch so as to fatten back up a bit—grossing everyone, including the bad guy, totally out.

Films -- Live Action

In Thunderball, both novel and film, James Bond locks his rival Count Lippe in a Turkish Bath, causing him serious injury and delaying the SPECTRE scheme in which Lippe was supposed to play a part. See also Villain Ball to know why Bond was fighting Lippe.
- Seemingly toyed with in GoldenEye - Xenia Onatopp tries to seduce and kill Bond in a steam room. The novelization implies that the heat plays more of a role in Bond's initial inability to fight back.
In the 2002 movie adaptation of The Count of Monte Cristo, the Count locks himself in a sauna with Monsieur Villefort and raises the steam to its maximum, interrogating him until the stress and heat combine to force Villefort to confess his culpability in the Count's imprisonment.
A pack of crooked doctors tried to kill Moe and Larry this way in "Monkey Businessmen", but Curly freed them by Turning It Up To Eleven and blowing the door off its hinges.
In The War of the Roses, being trapped in his own sauna is what almost kills Oliver Rose. Well, one of the many things. Most of them precipitated or planned by his wife.
Happens in the movie Daddy-O, which was featured on an episode of Mystery Science Theater 3000.
The Tanning Beds of Death from Final Destination 3 could be considered a less dated variant of this.
In What's New, Pussycat?, Woody Allen tries to do in friend/romantic rival Peter O'Toole by cranking up the heat in the steam room they're in. O'Toole thrives on the steam, and Allen nearly passes out (doesn't help that he's fully dressed, sportcoat, glasses and all).
A death trap operating on the same principle (though not made to look at all innocuous, as in some examples) was shown in Godzilla vs. Mechagodzilla.
Urban Legend: Blood Mary features the tanning bed variant. The character is essentially Stripped to the Bone by the heat.
In Master of the Flying Guillotine, the One-Armed Boxer lures the Thai kickboxer into a cabin with a metal floor that his students heat up with a bonfire. The floor burns the feet of the barefooted Thai, allowing the One-Armed Boxer to pummel him to death with ease.

Literature

Possibly referenced in Iorich, where Kiera has Vlad soak himself in a hot spring to soothe his aches after a beating. Once he emerges, she remarks that she'd heard Easterners' hearts would explode from that much heat, but she hadn't believed it.
The Fool of the World and the Flying Ship: the tsar locks the fool into his bathhouse and orders the furnace cranked up to kill him. The fool, of course, borrows his friend's straw that can soak up any heat and actually has to try to stay warm in the bathhouse.
Used against Nancy Drew in Two Points to Murder, when she's investigating a college basketball team and gets trapped in the sauna room. She winds up stripping to her underwear to buy time before finally figuring out an escape.
Journey to the West, the monkey Sun Wukong is put into a furnace. He survives though.
Phryne Fisher and Sascha are locked in a Turkish bath by the killer in Cocaine Blues.

Live Action TV

The Bookworm once locked Batman and Robin in a steam room disguised as a giant cookbook, saying it was a recipe for steamed bat.
- And it wasn't a sauna, it was hooked up to super-heated steam from a steam tunnel.
A live action example of the Sauna Box Death Trap: Number 6 finds himself trapped in one of these during an episode of The Prisoner. (It doesn't explode, though, he merely escapes.)
In The Adventures of Brisco County Jr., Brisco and Lord Bowler are tied up in a sauna, though the intended method of death is the exploding boiler rather than the heat.
In Powerhouse, one of the kids is taking advantage of a weight loss program run by crooks who were using it as a to get the bakery he was working at empty for a robbery with the neighboring bank. Deciding he had outlived his usefulness on the night of the job, he's talked into using their sauna, locks him in and turns up the heat full blast. Fortunately, he was able to manipulate a vent to signal SOS which his friends spotted and rescued him.
Shows up in an early episode of CSI, though the sauna only exacerbates a treatable injury to the point of death, and isn't used as a weapon in the strictest sense.
Appears on Kenny vs. Spenny in the "Who can wear a Gorilla suit the longest?" episode, though the endgame was to force the other participant to remove the costume (and lose the competition), not actually kill them.
Bizarrely used in Wonderfalls, when the sister and her rival are at the gym rivalling with each other. They then head to the sauna, where the sister storms out, accidentally locking the rival in the sauna. Later, it turns out that being locked in a sauna forced her to have a crazy Native American vision quest and become leader of her tribe, thus solving every single problem on that show. Hooray, logic!
- But that's how all the plots in Wonderfalls work. (That is, they all involve that sort of Rube Goldberg logic, not "every time someone gets locked in a sauna and has a vision quest.")
This happens twice in Spin City. In one example the only reason why most of the main cast was trapped in the sauna was because a nosy reporter was prowling outside. In another example, Stuart and Carter get trapped in the boiler room of city hall while trying to fix a circuit for a vending machine. Carter couldn't get the fuse box open, so Stuart grabs a conveniently located crowbar... which was being used to prop open the door.
- To make matters worse, at the end of the episode when Mike finally finds them, it's revealed that there was a phone in the room the whole time.
An early episode of Murder, She Wrote had Jessica in this situation.
Dark Justice. A Black Widow killer bumps off her first husband this way.
On an episode of The Chronicle, the tabloid reporters were dealing with the angry ghosts fat people killed in a fat farm sauna. In the end, they had to rescue the murderer from suffering the same fate.
This happens to Clark Kent in a Season 1 episode of Smallville, where the villain threw him in and barricaded the door. Of course, the sauna has kryptonite in it. He manages to break a hole in the door's window before he collapses, which saved him from dying until Pa Kent could rescue him.
Miss Fisher's Murder Mysteries: "Cocaine Blues": As in the book, Phryne Fisher and Sascha are locked in a Turkish bath to prevent them from revealing the truth of the drug enterprise being run through the building. She jams the steam machines in a bid for time, which causes an off-screen explosion once they're safely clear.

Theater

Raoul and the Persian get trapped in one in The Phantom of the Opera. To be fair, it wasn't exactly a "steam room" per se—more like a "heat-and-optical-illusion room", but it still qualifies.

Video Games

In one of the Hitman games, the player can kill one of the targets by blocking the door to his steam room and increasing the supply.
In Nancy Drew: The White Wolf of Icicle Creek, there is one puzzle where Nancy is locked inside a sauna.
Lunar Silver Star Harmony, the Goddess Althena is put into something similar.

Eiphel: Then believe what you will as you fade into nothing... in the flames of the Fornaceron!

In Persona 2, the party at one point in both games run into an oven trap on their way to stop the Masquerade.
The Gold Luger deathtrap in Resident Evil Code: Veronica.

Western Animation

A variation of the Sauna Room is the Sauna Box, which has been used in countless cartoons as a means for wacky anthropomorphic animals to dispatch their rivals. (Usually the cartoon animal locked in the Sauna Box has their head turn red as they get hotter. In more creative examples of this trope, their head will actually turn into an overheating thermometer.) This trope usually ends with the Sauna Box exploding in a spectacular fashion, or a radically reduced victim emerging from a cloud of steam..
In one episode of Rugrats, this happens accidentally, in what is apparently the worst-designed sauna in the world.
Totally Spies!: The girls were locked in such a trap by their Brainwashed mothers.
Happens in the Code Lyoko episode "New Order". XANA locks Yumi and Ulrich in a room and raises the temperature, making it a Death Trap, although the real point was to show the two avoiding looking at each other when they were forced to start taking their clothes off; as if their relationship needed any more UST.
The first attempt on the life of Homer Simpson in "The Great Louse Detective" by Frank Grimes Jr., in revenge for his father whom Homer drove insane. He was actually already in danger by being in the sauna at all because of his obesity and heart problems. The sauna controls helpfully included the setting "murder".
Subverted in Futurama, where Fry and Bender rupture a steam pipe in Zapp Brannigan's brig. When they're released, they've kicked back and are initially reluctant to leave.
Attempted on Inspector Gadget in the health spa episode.
In one of the Pink Panther show bumpers, Blue Aardvark was shrunk to ant-size by a steam cabinet. Charlie then chased him around for a while.

Real Life

Incredibly, this has actually happened. The World Sauna Championships 2010 in Finland ended in one contestant getting killed and another suffering third degree burns and falling into a coma for two months. Mind you, it was about a contest on being able to stand longest in the hottest sauna. An autopsy revealed that the contestant who died had used painkillers and anesthetics to bypass his physical limitations.
People sometimes do get killed in the sauna if they pass out because of an attack of disease or drunkenness.