Unsafe Haven

So you have this princess/person/item/whatever of great importance that you totally need to keep hidden or protected from the bad guys (or maybe even the good guys). Or maybe you need to go into hiding for a while and bide your time before you kick your enemy's big, flabby tushy. Well, no problem! There's supposed to be this place down the street that's said to be very safe from outsiders. Granted, it is only a few dozen meters from where enemy Mooks go on coffee break, but come on, no one will suspect a thing. Perfectly safe!

You can't argue with that, you say to yourself, so you put your undying trust into this safe haven of sorts, perfectly relieved to know that there isn't a snowball's chance in Hell that anything's gonna happen to OHWAITNO the Big Bad broke in and ruined everything.

Unfortunately, this "safe haven" was really a... well, unsafe haven—a supposedly "safe place" that is either glaringly penetrable or right in plain sight (or even both) that the Big Bad or the hero wouldn't even have a problem finding it or breaking in if he were blind. Or had his hands tied. Or if he were blind and had his hands tied.

One may wonder why anyone would bother using such terrible places for hiding/protection, but it is, nevertheless, quite an effective device to take advantage of to move the plot along, and it is also a commonly-used trope in fiction. It's likely to be of greater effect in lulling the audience into a false sense of security if the work in question is electronic or live-action—perhaps the heroes really have made it to safety—but, of course, there's no accounting for the savvy fans who look at their watch or the inventory screen, or the 500 pages left to go!

Contrast Cardboard Prison, where instead of the place of detention being laughably easy to storm or find, it's laughably easy to escape. Compare Neon Sign Hideout, when this trope is played for laughs and fails even more as a hide-out. See also Hidden in Plain Sight and Right Under Their Noses for when the heroes attempt to hide as close to the bad guys as possible, Swiss Cheese Security for when it's laughably easy to enter the villain's lair, and Ditch the Bodyguards for when the haven is safe, but the protectee refuses to stay.

Examples of Unsafe Haven include:

Literature

In Harry Potter, Hogwarts is supposed to be the safest place in the world despite the fact that there is apparently revolving door of evil. It's infiltrated every single year by the bad guys.
- Gringotts. It may be harder to break into than Hogwarts, but it's certainly not as infalliable as the goblins would have you believe.
- The Death Eaters' meeting in chapter 1 of Deathly Hallows basically consists of Voldemort saying "I think I'd like to infiltrate and take over the headquarters of the magical government." He succeeds almost immediately after, on his first attempt.
  - Considering the fact that Voldemort was able to easily and quickly take over any location he wanted, except Hogwarts, it might really be the safest place in the wizarding world. Let's not forget it was guarded by one of the few wizards powerful enough to fight Voldemort. It just wasn't 100% safe.

Film

Invoked in the Film version of Lord of the Rings as a Tropey shortcut to explain to the uneducated viewer why "The Ring cannot stay in Rivendell!" Throughout the first part of the film we are led to believe that "the Ring will be safe in Rivendell!"—until Elrond tells Gandalf otherwise. Oh snap! This is of course only in the film as a drama-preserving handicap for the sake of maintaining tension. In the books, and for the attentive viewer, Rivendell is obviously not the final destination.
Nanking in The City of Life and Death. The Safety Zone is repeatedly violated by the Japanese soldiers.
In the Disney version of The Hunchback of Notre Dame, one can apparently claim sanctuary in the church and not be harassed by the soldiers. Of course, that's only a paper-thin barrier for Frollo later on in the film.
In Hook, the Lost Boys' hideout is this, which the Nostalgia Critic noted, complete with a large arrow.

Critic: So he [Peter] goes back to the hideout...which really isn't a hideout; it's a tree with lights.

28 Weeks Later has the military lock all the civilians in a large-ish room "for their own safety". They leave a door unguarded. A single infected simply uses himself as a club to break open the door, run in, and... Hilarity Ensues.
In A Stranger Among Us two street thugs-not master criminals, not assassins, just thugs-are able to terrorize the Hassidic diamond district as if Jews were to stupid to keep security around diamonds. In reality of course the Shomrim(Hassidic security)would have tossed a mere two rather incompetent robbers out on their ear with a suitable amount of bruises.

Live Action Television

This is a very common trope in any Police Procedural involving a witness, to the point of enforcing No Good Deed Goes Unpunished throughout TV-land and implying that no witness in police protective custody is safe.
Lost has the Temple. It's a mysterious location alluded to throughout the early seasons; Ben Linus tells his daughter to go there because it will act as a safe place, in S4. But when the time comes for the Smoke Monster to get in, he manages this feat in less than an episode.

Video Games

The Legend of Zelda has had its fair share of this happening. For instance, in A Link to the Past, we have the aptly-called Sanctuary, where Princess Zelda takes refuge after Link saves her from confinement in Hyrule Castle. It's supposed to be a safe place, even though it's kind of in the open and that enemy knights are kind of on patrol outside. Why Ganon didn't find it and capture Zelda sooner, like before Link got the Master Sword, is anybody's guess.
- Hyrule Castle itself is also this in The Wind Waker. After the truth of Tetra being the successor to the Hyrulian Royal Family's bloodline is revealed, Zelda is kept in the same chamber that the Master Sword was kept. Of course, considering that Link cleansed the place of Ganon's forces only a few hours or so before, it was no surprise that Ganon found her.
Guild Wars: In the Nightfall campaign, two of the three Vabbian princes try to retreat to such a sanctuary. The players break in to get them involved in the war again, before the bad guys have a chance to reach it.
Any time a game forces you, the hero, to give up a MacGuffin or Princess you've rescued, they're as good as re-kidnapped. Such is the case of the Divine Rods in Okami. In this case you gave them to The Dragon while she was in disguise.
The Half Life games are a series of getting yourself to these... the surface, Lambda Complex, Kleiner's Lab, Black Mesa East, and White Forest are all places you are striving to reach for their relative safety... until you get there.
- Unlike everywhere else, White Forest is still in-tact when you're leaving it at the end of the Episode Two.
City of Heroes: The vault of the Modern Arcane Guild of Investigation (MAGI) is so prone to having supposedly safe macguffins recaptured after being locked in it that it has become a running gag among players.
New players in EVE Online occasionally start with the impression that high security space is safe. They learn very fast that it isn't.
The safe havens in Alan Wake are generally, well, safe, being cones of light that drive off the Taken. Except that the havens are powered, and if the power goes out while you're standing there....
In any Escort Mission, if the idiot you have to protect doesn't do something else, it'll be this.
Left 4 Dead is based on the group moving from one temporary safe haven to another in the hope that one location will be a permanent safe haven. And yes, the infected WILL break in if you stay in these temporary havens for too long.

Tabletop RPG

Dungeons & Dragons adventure I12 Egg of the Phoenix. After the Forces of Evil steal the Egg from Doc's Island, the PCs manage to retrieve it. The Council of Northending has them take the Egg back to Doc's Island, where it is put in exactly the same place and with the same security as it had before. Not surprisingly, the Forces of Evil manage to steal it again almost immediately.