Interdimensional Travel Device

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 and Inn Between the Worlds

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 the Paratime series by H. Beam Piper, the means of traveling through timelines is a conveyor using the Ghaldron-Hesthor field-generator. Conveyors are fixed in place, which means that as they travel through timelines, they may end up inside nuclear reactors or other hazards or be caught in warfare (a common activity on at least one timeline in nearly every trip, Paratimers note). Weakening of the transposition field is a concern of Paratimers.
 * 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: Several times:
 * The Lion, the Witch and the Wardrobe: has a wardrobe that allows travel between Earth and Narnia—sometimes.
 * The Magician's Nephew has the green and yellow rings, which allow one to enter the Wood between the Worlds and leave there for any number of worlds. The rings are mentioned again in The Last Battle.
 * 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.
 * In Parallax Hominids by Robert J. Sawyer, decoherence created by a quantum computer sends the neanderthal Ponter to a universe very similar to our own.
 * In Philip Jose Farmer's World of Tiers novels, people can travel between the artificial universes of the setting by using gates. Gates can be activated by various means, including tokens and playing music on a special horn.
 * The Wheel of Time has Portal Stones which, among other things, will let people travel between parallel realities.

Live Action TV

 * There are several "techniques" of universe-crossing in Fringe: Walter's portal, which causes both universes to begin collapsing; William 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 creating an Inn Between the Worlds. 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).
 * 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:
 * In Inferno, the TARDIS console transports the Doctor to a parallel universe where Britain is governed by Fascists.
 * In Rise of the Cybermen, the entire TARDIS travels to another parallel universe (usually referred to as "Pete's World") where Britain is a republic and zeppelins are in common use. In Army of Ghosts the inhabitants of Pete's World develop transporter medallions that can travel between the dimensions; later, they create a "dimension cannon" for the same purpose.
 * In The Monkees 1997 ABC special, Hey, Hey, It's the Monkees, we learn that Mike had turned the Monkeemobile into a dimension machine (AND lowrider, of all things). It's even capable of transporting them back to The Sixties.
 * 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.
 * Buffy the Vampire Slayer and Angel had at least one of these, Angel used it to travel to Jasmine's old home. And another was used to travel to Skip's holding dimension where Billy was being kept. The 'verse's portal books probably count as well.

Tabletop RPG

 * Dungeons & 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 Transdimensional 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.
 * Featured in MS Paint Adventures:
 * In Problem Sleuth, there two ways to travel between the real world and the world of imagination: Either climbing through a window, or entering a fort and imagining really hard (booze helps with the latter).
 * Homestuck features fenestrated walls. Normally they're used to observe faraway places, but smashing through the wall allows one to travel to the location. Andrew Hussie breaks through one of these walls to get from his house in Real Life to Doc Scratch's house in the trolls' universe. Later,.

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. See Schrodingers Cat
 * 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, including 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, including one where Fry and Leela are married.
 * On Teenage Mutant Ninja Turtles, the Turtles use the transdimensional portal, a technology that allows travel to alternate universes. It is most commonly used in the 1987 cartoon series. Another approach is used in Turtles Forever; the teenage mutant ninja turtles use a dimensional portal stick to go to the 1987 universe.
 * In Phineas and Ferb The Movie: Across the 2nd Dimension the Other Dimension-inator is used by Heinz Doofenshmirtz to go to the second dimension, as the title suggests.