Convenient Cranny

Bob is being chased and/or attacked by a Big Thing, which is probably some sort of monster. (The Big Thing can range anywhere from "10 feet tall" to "Friggin' Godzilla", just so long as it's bigger than Bob.) But Bob discovers a convenient hiding place, which protects him from the Big Thing because the Big Thing is too big to fit inside. This hiding place is called the Convenient Cranny.

The Cranny may be something like cave with a narrow entrance, or a doorway, or a gap between tree roots, or whatever. Often, the Big Thing will claw or dig at the edges of the Cranny's entrance, but this rarely works. Bob may now be effectively trapped in the Cranny until something kills or distracts the Big Thing, or perhaps the Cranny has a back door of some kind which allows Bob to get away on his own.

Compare Behind a Stick or Escape Convenient Boat. May overlap with Try and Follow.

Examples of Convenient Cranny include:

Anime and Manga

At one point in Fullmetal Alchemist, Ed manages to survive being crushed by a rolling ball of death due to his small size allowing him to squeeze into the corner of the hallway he is walking down... Then he feels relieved about being the height he is before he starts complaining about himself accepting that fact.

Comic Books

Bone: Fone Bone, those Stupid Stupid Rat Creatures, Bartleby, Smiley Bone, and all the orphans attempt to escape Kingdok in one of these.

Film

Seen in the film Avatar when Jake flees from the creature near the beginning of the film. He ends up ducking into some sort of Hammerspace under a tree, but his hiding place is not that effective; the beast still manages to claw at him fairly decently.
Luke does this in Return of the Jedi, getting a breather from the Rancor... just long enough to plan his exit.
Emmett hides from an alien in one in Cowboys and Aliens.

Literature

In the first Harry Potter book, there is a scene that could count as this. After managing to subdue the humongous three-headed dog, Fluffy, the trio drops down a hatch to escape the dog. Of course, this did not turn out to be as convenient as it may have at first seemed.
Dune - while Paul and Jessica are fleeing a Sand Worm, they find a crack in a cliff and successfully hide from it.
In Clan of the Cave Bear five year old Ayla hides in a cranny to escape a Cave Lion. The lion can just manage to stick its paw in to slash Ayla on the thigh, thus marking her totem.
Binks of Hezabad in Municipal by Rudyard Kipling met a mad elephant and had to... why, just read it.
In the novel Jurassic Park, one of the kids hides from a Tyrannosaur in a convenient cave behind a waterfall. The Tyrannosaurus then proceeds to pull the child out with its tongue. Fortunately the tranquilizer it was shot with earlier kicks in just before it pulls the kid into its mouth.

Video Games

When the Player Character can do this in video games, Cherry Tapping can often result. An example of this would be The Elder Scrolls: Oblivion - you can hide in the tunnel to the arena and shoot hundreds of arrows at the minotaurs who can't reach you.
Primal - When The Dragon Belhazur shows up, Jen hides in a Convenient Cranny while Scree possesses a statue for the Boss Fight.

Western Animation

Occurs in The Lion King at one point. As a cub Simba runs from the stampede, hyenas on his tail, he squeezes through a tiny passageway. One of the hyenas swipes its claws where he vanished just moments before.
During A Bugs Life the current 'gang' has to duck into a rather convenient bush to avoid a hungry bird.
The Fox and the Hound (film) (the animated version, if you didn't gather that) also demonstrates this trope. Todd and his new mate dive into a burrow to avoid the snapping jaws of Copper. However, this cranny proves useless when the hunter finds a way to drive them out.
Meet the Robinsons .. when the Big Bad brings a T-Rex into the future, it's unable to attack Lewis when he stands in the corner of a building.