Interdimensional Travel Device/Sandbox

Probably Needs a Better Name.

A device that allows travel between dimensions/alternate universes/planes of existence/etc. This device could be anything, from a machine in science fiction to a magical item in fantasy, as long as it allows travel between these dimensions or realities. It could even be a human (or, at the very least, a sentient being), if they have the power to go to these other "places".

Compare Time Machine.

Film

 * The One has a quantum tunneling device which allows the interdimensional police to track criminals and, obviously, allows them to travel to different universes.
 * Crossworlds has a staff which can get the main characters from the odd world from which the staff comes and back to what appears to be our Earth.

Literature

 * In Robert Heinlein's The Number of the Beast, Professor Jacob Burroughs creates a device that allows travel between dimensions. It's installed in a vehicle and allows the protagonists to go on a series of adventures.
 * The Dark Tower series has doors that allow the characters to travel between different timelines and alternate universes, including one in which.
 * The Chronicles of Narnia One of the most well known examples, has a closet that allows for travel among multiple universes.
 * The Transition Of Titus Crow has a clock that allows Titus Crow to travel to different dimensions
 * His Dark Materials has items that allow for interdimensional travel
 * Myth Adventures has the D-Hopper which is used throughout the series to get to different universes.
 * The Incomplete Enchanter by L Sprague De Camp and Fletcher Pratt introduced the Syllogismobile which attuned the practitioners' minds to a selected alternate universe strongly enough to shift them into it.

Live Action TV

 * There are several "techniques" of universe-crossing in Fringe: Walter's portal, which causes both universes to begin collapsing; Leon Bell's technique by which he pulled Olivia into the AU (usually only works on hybrid Super Soldiers who are designed to survive the crossing; it worked on Olivia because of her Cortexiphan-enhanced physiology); and the natural way, which is achieved by groups of Cortexiphan Kids being guided by Walter (and of the three, is clearly the least dangerous, to dimensions and dimension-crossers, but not without its kinks). Besides crossing, peter is able to use the device created to only work with his genetics to bridge the to universes. This unlike the other devices such as Walter's portal device has no know negative side effects. Another less used method is the harmonic rods which create an equilateral triangle enveloping the subject on both sides, and have the rods vibrate at the same frequency, and two objects of approximately equal mass will exchange places in space-time. There are many ways to mess this up though, such as only placing the rods in one universe.
 * Stargate SG-1 has the "quantum mirror", which makes a few appearances in early episodes before being destroyed offscreen, on O'Neill's orders. In one episode, Daniel accidentally uses it to travel to another universe; in a later episode, alternate-universe versions of Carter and Kowalski come back through it, looking for refuge from the Go'a'uld invasion fleet that just arrived on Earth in their universe.
 * In Stargate Atlantis, an alternate McKay builds an "alternate reality drive" which has this function. The only problem is, it doesn't have an off switch or any way to control which reality it jumps into. This leads to one universe's worth of main characters being stranded in the wrong reality and another universe's worth dying of starvation before they can figure it out, before the actual main characters bootstrap on their research and discover a way to make it backtrack through the realities it came from (so they can at least get home, if not actually exploit the drive).
 * In Terra Nova, the portal links the in-universe 2149 Earth to Earth 85 million years in the past. However, it's later discovered that the two Earths are in separate timelines so that it's not time travel in the conventional sense.
 * Sliders had the "Timer", several of which were actually used by the main characters (the original, the one from Egyptian World, and Colonel Rickman's Timer). The Timer's job was to open wormholes between universes, and also to malfunction or get stolen, providing half the series' plots.
 * In Doctor Who, medallion-like devices can be used to travel from the universe of the "Cybus Cybermen" and back to the main universe, though there has to be an open gateway to the void between universes (or the collapse of reality) for them to work. Daleks used a Void Ship to enter the void, escaping the Time War and later escape into the universe, while the Cybermen later used the Daleks' dimension vault to escape being trapped in the Void.
 * In Star Trek, transporters under the right circumstances can be used to travel between dimensions. One way is to add a device to the transporter that reconfigures it for this use.

Tabletop RPG

 * Dungeons and Dragons has had a number of such devices, like the Amulet of the Planes and the Cubic Gate.
 * There's way more, from portals disguised as mirrors and ordinary doors that only activate when a certain combination of objects (a "portal key") are presented to them, to various high - level spells that can take you to such places as the Astral Plane, the Plane of Elemental Fire, or planes that house the afterlife.
 * Module Q1 Queen of the Demonweb Pits. A temple in a Drow city has a mural of a starry sky. If the PCs pass through an image of Lolth and touch it, they will be transferred to the level of the Abyss where Lolth's Demonweb exists. Once there they can find doorways to alternate Prime Material Planes as well as the Abyssal level where Lolth's spider ship awaits them.
 * Module X2 Castle Amber. The Gate of the Silver Keys takes the PCs from Glantri in the Known World to the dimension where the country of Averoigne exists.
 * Paranoia had the Trasndimensional Collapsatron, which allowed travel between dimensions in several adventures.

Toys

 * In Bionicle, the Olmak can do this.

Web Comics

 * In Dragon Ball Multiverse, some guys called the Vargas have this, as they're able to cross between universes (timelines). They come from a different universe than the one the protagonists live in, and they offer them a chance to participate in a tournament among fighters from different universes.

Web Original

 * In Blackbird's Aniverse setting, the hammerspace drive, which can fit in a character's pocket and allows travel into Hammerspace, which connects various zones in different dimensions. For example, in the "Kawaii" dimension, there's a Happy Bunny Forest zone, which is an entire universe filled with Exactly What It Says on the Tin. In the "Boring" dimension, there's Tokyo Prime, a universe where Tokyo is the center of everything, but nothing ever happens there, and so on.

Video Games

 * In Chrono Cross Serge uses kids astral amulet to travel between his world and the other world which was created 10 years ago due to a universal split where Serge is alive in one universe and dead in the other.
 * In Crash Twinsanity the psychetron created by Dr. Neocortex can travel between Crash's world and the 10th dimension and most of the game is based around gathering the power crystals needed to power the device so Crash Bandicoot can get to the 10th dimension to save his world.

Western Animation

 * Family Guy Stewie invents a remote control that can travel to many universes and one where meg is hot, but still ugly compared to everyone else.
 * Futurama Professor Hubert Farnsworth invents the parabox which allows travel to different realities,