Locked Away in a Monastery

A trope often found in a Standard Royal Court: When someone in power (e.g. the monarch) wants a person (e.g. an heir, a spouse, or a favorite) removed from public sight but are unwilling to kill them (e.g. because of Royal Blood, or because they actually just want to protect them), they will make them take the vows at a remote monastery/nunnery. This way, the newly-made monk/nun will be permanently restricted in movement and any voluntary or assisted attempt to return to secular life will be considered a sacrilege. Also, celibacy means they won't have children.

In a less permanent variation, monasteries are also a popular choice for wealthy families to place their daughters in until they marry: a monastery means strict upbringing, education, and more or less guaranteed virginity. Bonus points for not needing to provide the kid with class-relevant and expensive dresses while she is kept there.

Sub-Trope of The Exile, Reassigned to Antarctica, and Kicked Upstairs (in the sense that the failed courtier of earthly monarchs is now serving the Lord of Heaven). Related to Man in the Iron Mask and Gilded Cage. Not Get Thee to a Nunnery, where it appears that someone is threatening a woman with this but it is actually a Double Entendre.

Comic Books

 * Borgia Power And Incest does the safekeeping variation to Lucretzia. She's fetched back for her marriage: "Miss Lucretzia, I left a little girl here and in her place I find a beautiful young woman..."

Literature

 * In Arcia Chronicles, Charles Tagere wanted to do this to his hunchback son Alexander but died before Alexander came of age. Charles' heir then overruled his father's decision and made Alexander a general.
 * Also, this trope always goes horribly wrong with women who are sent to become nuns of the Cialinan Order: the Order is, in fact, an Ancient Conspiracy of power-hungry witches.
 * This happens to Amena, Count D'Elmont's first "love" in Love in Excess.
 * Happens to one of the corrupt Arendish somethings in one of the Belgariad/Malloreon/whatever prequel novels.
 * In The Elenium this was the punishment of Arrissa, the very wanton sister of the previous king. She was sent to a convent because she couldn't be executed, and made life miserable for everyone. She kept hiding raunchy woodcuts in prayerbooks.
 * This ended up backfiring on the main characters. The convent was lightly defended and the nuns were massacred when Arrissa's accomplices sprung her.
 * The Highborn in Chronicles of the Kencyrath sends those who are too obviously Shanir (ie weird) the Priest's College and out of the way.
 * Angelina Dorma is sent to a nunnery in the end of Shadow of the Lion.
 * Subverted in The Religion.
 * Eventually happens to Maria Clara on Noli Me Tangere.
 * A rather long subplot in The Forest of Hands and Teeth focuses on the protagonist joining the Sisterhood because she has no other options in her outrageously strict society, although she desperately does not want this. Subverted because, like everything else in the novel, it goes horribly awry.
 * In the original Hans Christian Anderson version of The Little Mermaid, the prince falls in love with a young woman from the local nunnery who finds him shortly after the mermaid pulls him from the water. Resigned to never being with her, the prince considers marrying the mermaid, when it is revealed the young woman was never a nun, but a princess being educated there. They marry and live happily ever after. The mermaid...not so much.
 * In Sharpe's Honour, la Marquesa de Casares el Grande gets confined in a convent so she can't contradict the faked evidence that's supposed to convict Sharpe for murder.
 * This is common as both a threat and an actual practice in the Videssos books. Not surprising as the Empire of Videssos is the Byzantine Empire with magic.
 * In A Song of Ice and Fire, The Night's Watch is frequently used for this purpose. While it's a military order, its location on the edge of civilisation in the frozen North and the vows of chastity and non-inheritance its brothers take mean that anyone sent there is rendered fairly harmless. Sam Tarly, in particular, was ordered by his father to join the Watch so that his much younger brother could become the heir in his stead. The possibility of his joining religious or scholarly orders was raised, but brusquely dismissed by the extremely militant father.

Live Action TV

 * In the Degrassi the Next Generation two-parter "Accidents Will Happen," Manny (a Filipino-American) is terrified of telling her parents about her pregnancy, because she doesn't want to end up like her cousin back in the Philippines who got sent to a convent.
 * In Pushing Daisies, Aunt Lily sends Olive to a nunnery to protect the secret she accidentally blabbed, although that lasts for a very short time. And Aunt Lily knew about the nunnery because she was sent there herself as a youth to hide a pregnancy.
 * The Cadfael series uses this at least once or twice.

Theatre

 * Mentioned in Shakespeare's Much Ado About Nothing: When Hero has been denounced as unfaithful, the priest's Plan B is to quietly ship her off to a nunnery where she can live out the rest of her days in anonymity.

Video Games

 * In the Mass Effect series, Asari with the Ardat-Yakshi genetic defect are given a choice between this trope and execution. That's because Ardat-Yakshi are effectively succubi and their condition causes them to kill people by mating with them.
 * This can happen in Crusader Kings. It's treated just like death.
 * Final Fantasy Tactics: Princess Ovelia spent her childhood being brought up in a monastery before the plot started.
 * In Dragon Age: Origins, Alistair, a bastard son of, was sent away to a monastery at age 10 for safekeeping and joined The Order of Templars later.
 * Sebastian, third prince of Starkhaven in Dragon Age II, was given to the priesthood in his late teens for being a complete embarrassment to his family. Unusually for this trope, he grew to like his new state and matured rapidly into one of the most reasonable party members.

Real Life

 * Subversion: Louis VII was sent to a monastery for safekeeping until the intended heir died, and he had to brought back.
 * Was popular in Russia during multiple coups, mostly as a way to dispose queens.
 * A common way for a Byzantine emperor who could see the end coming to depart with his eyes intact was to abdicate and join a monastery, knowing that the monastery is where he would end up anyway.
 * The Carolingian Pepin the Short, upon seizing the throne of the Frankish Empire, promptly sent his Merovingian predecessor Childeric III and his son Theuderic to a monastery, to get rid of any potential rival claimants. The fact that the supposedly less-civilized Franks used this expedient—rather than the aforementioned Byzantine (and supposedly more Christian) eye-removal—to get rid of rivals to the throne has not been lost on historians.
 * The brother of "Bonnie Prince Charlie" (who would have been the heir to the Jacobite claim) monasticised himself as an official declaration that he knew when to fold em.
 * There are multiple subversions from Japanese history (most notably in the years 1086 to 1185) where emperors abdicated to join a (Buddhist) monastery. This was a political machination generally intended to keep power for themselves, acting behind the scenes.