Spirit World

The spirit world is the home of spirits and archetypes, little gods, ancestors, totems, elementals, angels and demons, embodied allegories and symbolical mindscape. It can get quite crowded if All Myths Are True, but fear not, the setting metaphysics will be usually more restrained than that.

Sometimes characters can reach it when they have an out-of-body experience, when they enter in a trance (with or without drugs) or when they use shamanistic magic or Psychic Powers to project themselves into the astral plane. They can go there to meet their Spirit Advisor, increase their power, go in a spirit quest, learn invaluable information and get cryptic advice.

Any show of the spirit world is sure to feature some level of Mind Screw and Rule of Symbolism, run high on Motifs and be under the sign of Absurdity Ascendant.

Compare with the Dream Land and Journey to the Center of the Mind. Not to be confused with Dark World. See also Magical Underpinnings of Reality.

Anime and Manga

 * Death Note; The shinigami realm is similar to this, except that no human character ever enters it and it's darker than most examples of this.
 * Kamichu! has one of these. It looks like an Edo-period city, and is populated by various Shinto critters. Under certain circumstances, similar critters can be found operating the underpinnings of our perceived world as well.
 * Berserk features five different planes, whereof one is the classic spiritual plane. This picture explains it better then I can.
 * Spirited Away has a protagonist who gets trapped in such a setting.
 * The oft-referenced "C's World" from Code Geass; when
 * Nayug, the spirit world of Moribito Guardian of the Spirit seems very alien but magnificent to cast and viewers.
 * Yu-Gi-Oh! and it's sequel series feature worlds where Duel Monsters are real. GX reveals that there's a grand total of twelve separate dimensions populated by real Duel Monsters.
 * In Bleach the plot is dominated by the two warring spirit worlds: Soul Society, home of the Soul Reapers and the Heuco Mundo, stronghold of the Hollows. There exist three other spirit worlds of differing importance. One is the Palace Dimension of the Spirit King, ruler of Soul Society, that only Squad Zero and the Captain-Commander can access. The second is Hell, the destination of any spirit that has committed heinous acts before their death. The third is the Valley of Screams, a dimension where souls awaiting rebirth gather and shed their memories.
 * Dragon Ball (and Z and GT) has what is usually translated as "the Other World." It includes Heaven, Hell, and the places in between where all sorts of spirits, gods, and otherworldly bureaucrats spend their time. The spirit world even has a spirit world of its own, the Kaioshin Realm, a place too holy even for residents of the spirit world. There's also a demon realm somewhere.
 * Amatsuki, although it's ambiguous as to whether it's all an illusion. Or perhaps even an illusion within a dream.

Comic Books

 * In The Authority, The Doctor has a Spirit World where previous incarnations of The Doctor act as Spirit Advisors.

Literature

 * The Nevernever from The Dresden Files, suspiciously similar to the Umbra. It contains Faerie, the realms of various demons and Eldritch Abominations, and possibly heaven and hell to boot.
 * In the Nasuverse, the Spirit World is just another layer on top of the "physical" world -- the only things that humans can interact with would be those with enough power to physical manifest (eg. True Ancestors). Humans with supernatural perception can see a bit more than the Muggles.
 * Dunmanifestin in Discworld acts as a Spirit World in that the gods all live there.
 * The gods of Nehwon (home of Fritz Leiber's Fafhrd and The Gray Mouser) live in a Spirit World.
 * The Other Place in The Bartimaeus Trilogy, which we finally get to see in book three, Ptolemy's Gate.
 * In the Fan Fiction, Megaman Star Force Orion, Amaya Takeshi is sent to the spirit world in a couple of scenes to regroup. In both of those instances, he gets a pep talk from Yusuke from Yu Yu Hakusho, and Excel from Excel Saga returns Amaya to his home world.
 * In American Gods it's known as "backstage".

Live-Action TV

 * Buffy in Buffy the Vampire Slayer went in a spirit quest during season 5 to meet the First Slayer.
 * An episode of Northern Exposure saw Ed visiting a trailer park full of personal demons (Codependency is arguing with his wife, External Validation has a huge fancy car, etc.)

Tabletop Games

 * The Umbra of the Ol World Of Darkness was an big example of the anything goes version.
 * The Hisil (Shadow Realm) in the New World of Darkness is a more restrained and horror-focused version of the Umbra.
 * The Omphalos (collective subconscious) and Anima Mundi (the dreaming earth / soul of the world) in the Mage:The awakening supplement to World of Darkness are likewise examples of this, housing Archtypes, gods and demons, more-real-than-real flora and fauna and representations of magic itself.
 * Shadowrun magicians can project themselves to the Astral Plane.
 * Earthdawn: the most powerful mages can project themselves to the Astral Plane. It is much more dangerous than Shadowrun, due in large part to the Horrors that make the place their home.
 * The Warp of Warhammer 40000, one-third Spirit World, one-third Hyperspace Is a Scary Place, one-third Cosmic Horror.
 * In Dungeons and Dragons, primal classes can call spirits from the spirit world, which is described as a usually invisible layer on the natural world.
 * Rune Quest has shamans whose powers depend upon entering the Spirit World and battling/binding spirits. In Glorantha, the other main schools of magic (Divine and Sorcery/Wizardry) have their own equivalent otherworlds (God Plane and Essence Plane). Gloranthan characters enter Hero Quests on the God Plane and take on roles in myths to gain insights or magical power.

Video Games

 * Prey uses this as a plot element. After protagonist Tommy's grandfather dies, and Tommy himself has a near-death experience, he's pulled into the Spirit World to meet his grandfather again and learn how to spirit-walk.
 * Dragon Age has The Fade, where demons and other spirits rule. The spirits of earthly humans and elves go there in dreams. Mages can also enter The Fade using special rituals, but must be wary against demonic possession. While souls can be trapped in The Fade beyond death by particularly powerful spirits or demons, the dead do not generally go there. Not even the spirits know what lies beyond, though many, perhaps because their kind subsides on the positive (or in the case of demons negative) thoughts and emotions of mortals, believe in the god(s) of mortal religions.
 * Jade Empire has multiple heavens and other spirit realms.
 * Magical Diary has The Other World, home to all manner of supernatural beings.
 * Link can visit them in Skyward Sword. They are known as "Silent Realms" and are pretty dang creepy areas where pretty much everything is hostile (this isn't to say the Zeldaverse spirits are an inherently hostile bunch, these particular spirits are testing Link).
 * It's probable that the Silent Realms are parts of the Sacred Realm, the original resting place of the Triforce, because the place the Triforce is found looks and behaves exactly the same, except for the psychotic guardians. The Sacred Realm appears in many Zelda games, but it's usually a Dark World due to Ganon's influence.
 * In Mardek, dead spirits go to an afterlife similar to the Dreamrealm, but this time they're in control of the dream. As such, there are a number of "necropolises" there, composed of the collective expectations of various religions, etc. Also, guilty souls get to spend some time in the Anti-life until they come to terms with themselves, and virtuous souls have the option of becoming one with ARIENDEEN, the god of light.

Web Comics

 * The spiritual plane is where ancient spirits come from and generally reside in Circumstances of the Revenant Braves when they aren't in a pact with a human. However, no human characters have journeyed there . . . yet.
 * Gunnerkrigg Court has The Aether or The Etherium, which seems to be the same thing. Magic-using individuals can see there, with non-etheric objects becoming grey and powerful beings and objects remaining or becoming colourful and bright.
 * In the Foley house (Gillitie Wood emigrants in mostly human bodies) the lesson appears to be the whole class rapid-typing the equations of orbital mechanics -- for a mundane sight. But then Annie realizes if these students are this diligent for longer than ten seconds, there's something wrong and takes a look....
 * In Sluggy Freelance the Main Characters go to one of these in the Story Arc "A Time for Hair-Raising."
 * The astral plane of Concession has been compared to the internet, locations within it seem to be created by the spiritually aware. And considering that most of the time it's shown so that the Villain Protagonist can Mind Rape someone.
 * In El Goonish Shive, the spiritual plane is an ephemeral plane of existence parallel to the main universe. The beings known as Immortals live in it and normally it, everybody and everything on it is invisible and intangible to denizens of the physical plane. However, those on the spiritual plane can see and hear the physical plane and interact with those on it magically such as through their emotions. What the spiritual plane is not is a place for the dead; neither heaven nor hell nor the spirits of dead characters have been seen there.

Western Animation

 * Aang in Avatar: The Last Airbender will sometimes go there via meditation to talk to his past incarnations.
 * The Spirit World is also home to many entities that show up in various forms of animals, but are clearly intelligent and varied individuals. Strangely, most of these spirits take the form of regular animals like pandas with the occasional Talking Animal in the mix while the "real" world mostly has Mix-and-Match Critters.