The Hedge of Thorns

"A forest of thorns shall be his tomb!"

—Maleficent, Disney's Sleeping Beauty

A classic trope usually seen within the Fantasy genre, the Hedge has both a literal and metaphorical purpose within any story that features it.

Physically, it is a place of painful passage, thorns and brambles, that acts as a hazard for the main character(s) as they try to either pass it, or escape it. More often than not, it is connected to fairies (Fae) or some other mysterious group of creatures, as the trope is linked to the idea of a natural barrier to some greater prize (or terrible horror). Fantasy-wise, the Hedge usually appears within enchanted forests. However, sometimes the Hedge is conjured by a "higher power," and thus can appear anywhere the summoner demands (though not the golden rule). Also, the thorns tend to quickly eat whatever dies or lets its guard down within it.

The Hedge is most often a home for various forms of life, whether carnivorous or not. Sometimes it's a kingdom in-and-of itself, being ruled by an Overlord, Sorceress, Bandit King or similar character. Outside of the previously stated genre, the Hedge can be a torturously difficult labyrinth made from plants and fugi, or a hideaway for smaller characters against the Big Bad.

Metaphorically, however, the Hedge of Thorns can stand for something that tears at the psyche as well as the body of anyone who tries to get through it (fairies often are linked to madness). It also acts as a test of character, since it can stand between the Hero(ine) and the Bright Castle that holds what (s)he seeks. Usually the ordeal of the Hedge, as previously stated, is one of mental endurance and brinking on insanity, since it questions one's principals and bravery, as well as capability to adapt to the harshness of the reality that exists within the Hedge.

Note: the Hedge can also be a catch-all term for lands belonging to the Fae, such as the The Lost Woods.

Examples of The Hedge of Thorns include:

Comics

Castle Waiting is sealed off by one of these. Fortunately a tunnel has been cut through, although it's still an unpleasant experience thanks to the skeletons of people who didn't make it through still caught up in it.

Fairy Tale

"Rapunzel" has thorn bushes growing at the base of the tower, on which the prince is blinded near the end of the story.
Sleeping Beauty's castle is surrounded by roses. Many princes have met miserable ends in them.

Film

Willow uses some magic to burn a hole through the otherwise impassible wall of brambles.

Literature

A hedge also separates the faerie world from the normal world in Robin McKinley's The Door in the Hedge. In that case, it's a fairly normal hedge.
In Neil Gaiman's Stardust there is a stone wall dividing human world from the world of Faerie. It is not easy to get through and it has an enchanted forest behind it, though it is not literally a hedge (however, interestingly, the surname of the main character who is a half-fairy, is 'Thorn').
In Summer Knight, near the end of the story a Fey conjures up a nasty, poisonous hedge to keep Harry from interfering.
In One for the Morning Glory, Amatus invokes this as an analogy of their situation.

"This is not how these tales end," Calliope said firmly.
"This is not the way that things end when they get to be tales," Amatus said, "but since ours is not told yet, we cannot count on it. There were a hundred dead princes on the thorns outside Sleeping Beauty's castle, and I'm sure many of them were splendid fellows."

In Teresa Frohock's Miserere an Autumn Tale, the Rosa acts as this. Fortunately it's one of the good guys.

Tabletop Games

The Hedge from Changeling: The Lost, which is the border between the "real world" and the fae world of Arcadia (not in any way to be confused with the trope of the same name). There are actual thorns and a wide variety of other dangerous features, including living creatures, and it's generally an unhealthy place to be. Oh, and getting dragged through those thorns as a human rips your soul to pieces, which you then (possibly) only gather together once you escape from Arcadia.

Video Games

The magical hedge surrounding the Beast's abode in King's Quest VI.
Donkey Kong Country 2 had a few levels set entirely in brambles, famous for its Awesome Music: "Stickerbrush Symphony". They really do act as a test of character, because they're all really freakin' difficult.
World of Warcraft has a pair of dungeons called Razorfen Kraul and Razorfen Downs that are both built under a network of huge, thorny trunks. The occupants aren't faeries, though: they're savage boar-people, and the thorns aren't all that difficult for a player to get through.

Web Comics

In No Rest for The Wicked, Prince Ricardo tackles one.
Girl Genius has some as a part of Mechanicsburg defenses. Of course, these were made by a Mad Scientist against other Mad Scientists, so the stalks are studded with big metal spikes and can easily lift armored vehicles when raising.

Western Animation

The Ur Example is the thorn bushes growing around the castle in Sleeping Beauty.