Portable hole (Dungeons & Dragons)
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In the Dungeons & Dragons fantasy role-playing game, a portable hole is a magic item. It generally resembles a circular cloth which is placed on a surface to create a hole. If placed on a wall, for example, the user could access a 10 foot cube of space in another dimension for anything from storing items and objects to living in. However, if closed with a living creature inside without some form of air supply, they are likely to suffocate. In another instance, if the hole was placed on the ground, the user might be able to insert objects into it or allow others to fall in, as if he or she had dug a hole.
Portable holes were categorized by the circumference of their opening and their depth. Thus, a hole with a 1 foot circumference and 3 foot depth would be perfectly fine for burying or extracting some small treasure.
Some Dungeon Masters allowed portable holes to be used as weapons, saying that if the hole was affixed to a living being it would cause whatever innards it covered to spill out. Also, a living being put into the ground via a portable hole would be buried alive and die of suffocation.
Like a bag of holding, other portable holes, bags of holding or extra dimensional spaces placed in it would cause catastrophic results at the DM’s discretion. For example, a portable hole placed in a bag of holding might tear the bag, turning it into a bag of devouring.
In 1995, Issue 221 of Dragon magazine included an article "(More Than) 101 Uses for a Portable Hole" that discussed various approaches to the physics of a Portable Hole as well as listing innovative uses (a telescoping tower, portable apartment or workshop, connecting two to form a "tunnel," etc.) to which such a device might be put.
Second Edition/Third edition
In D&D 2.5 to 3.5, a Portable Hole placed on a flat surface did not open into the space behind it, but rather an extradimensional space 10 feet deep and as wide as the Hole (generally 6 feet in diameter). Every Portable Hole has its own particular extradimensional space. Anything placed inside this space remains there when the Hole is closed, and can be retrieved when the Hole is again placed on a flat surface. The extradimensional space when closed contains enough air for one Medium creature to survive for 10 minutes.
If a bag of holding is placed inside a portable hole, a rift to the Astral Plane is formed. This rift sucks in the bag and the hole, and they are lost forever.
If a portable hole is placed within the bag, it instead opens a gate to the Astral plane, sucking in every creature in a 10 foot radius, and destroying both the bag and hole. The contents of the bags are either scattered throughout the Astral Plane or destroyed.