The Multiverse
Multiverse is a term given to the cosmos by many spiritual paths, it describes the fact that the “universe” is actually multi layered rather than just a single plane of existence (Uni means one). To the Druid, Shaman or other spiritual person, the cosmos is usually seen as having three separate yet intertwined realms.
The Three Realms 
The World Tree Exploring the Other Worlds
The Three Realms
To the Celtic peoples, the world that we see is divided into three realms, that of the earth, the sea and the sky, or as we often call them, the middle, lower and upper worlds. Please click on a title in the image above to find out more.
The Sky
The Sky is the Realm of the Gods, The star beings, Bird Spirits and other beings that we naturally associate with the heavens. In some cultures it is said that the Upper World is a place of plenty, a warm and beautiful place where it's always Summer. We can easily see how the Judeao based religions have come to see this as the resting place of the immortal soul and the dwelling place of Yaweh (God).
The Earth
Of course the realm that everyone has access too is the Middle world of Earth, but lying alongside the "oridnary" world we find a spiritual level that the magically aware are able to tap into at will. This is the dwelling place of the living and of those that may not have moved on to wherever they need to go (Ghosts). We also find beings that might normally be seen in the other two worlds here as they travel about. Some may even have taken residence here. Here we also find beings that we call the fey folk (Faeries). In this spiritual layer we become startlingly aware of how everything is alive as we are able to communicate with the spirits of mountain, tree and stone, of badger, wolf and ant, in fact with the spirits of everything.
The Sea
To the Christian, the words "lower world" or "under world" conjour up images of Hell, of a place beneath our feet, caverns of firey torture and eternal damnation. However, this place "Hell" is but one area of the Lower World. In fact there are places in the Land beneath the sea that are pure paradise. Here we find such spirits as the ancestors, we find the old, primordial gods of creation and, yes, if you look hard enough, the nasty little beings that cause mischief and mayhem.
The World Tree
The Three realms are held together by the world tree, this unicersal image appears in shamanic cultures across the globe. Perhaps two of the more famous representations of the world tree are that of the Norse Ygdrassil and that of the Kabbalistic Tree of Life. It is said that the world tree has it's roots in the lower world and it's branches reach far up to support the upper world. Sometimes the World tree is home to certain creatures such as the Norse Ratatosk, a squirrel that runs up and down the trunk and tries to cause trouble between the Eagle who sits at the Top and the Dragon, Nidhog, who lives at it's roots.
The world tree is the axis of the world, the very centre and Shamanic figures from all cultures climb up or down it to reach the other worlds whilst on their journeys. In many cultures, the initiation ceremonies of the "Shaman" often includes the planting or building of a ceremonial tree which the "Shaman" and his/her teacher climbs to reach the upper world and recieve his/her initiation proper.
Exploring the Other Worlds
In order to take a deeper look at the Other Worlds we're going to take a brief look at the Norse View of the Cosmos, but to do this I'll briefly explain the Norse creation Story.
In the beginning there was a vast void known as Ginnungagap (meaning "magical power-filled space" or “seeming emptiness”. To the north lay a place of intense cold known as Niflheim and to the south lay Muspelshiem, a place of intense heat. Deep inside Niflheim lay the spring Hvergelmir. This spring gave rise to eleven rivers known as the Elivagar. Over many ages, the waters of the Elivagar ran across Niflheim and poured into Ginnungagap. The water froze, and turned to sheets of ice. Hot air from Muspellsheim melted some of the ice, creating melt water amid the ice. It was in this water that the first being, a giant know as Ymir was born. From Ymir was born the first race of giants, one of his legs fathered a son with his other leg while a giant and giantess came from under his armpit. As the ice continued to melt the divine cow Audumla was created and from her udders flowed rivers of mile which nourished Ymir. Audumla herself was fed by licking the hoar frost and salt from the ice. After three days, Audumla had licked the ice into the shape of a man and this became Buri, the first god.
Later in the Story, three grandsons are given to Buri, their names are Odin, Vili and Ve. These three set about killing Ymir and all but two of the frost giants were drowned in his blood.
From Ymir's body the brothers created the heavens and the earth. They used the flesh to fill Ginnungagap. His blood became the lakes and seas. From his unbroken bones they made the mountains. Ymir's teeth and the fragments of his shattered bones became rocks and stones His hair was used to make the trees, and his brains became the clouds. Odin and his brothers lifted Ymir's skull up and made the sky from it and placed a dwarf under each of its four corners, the Dwarves were called Nordri, Sudri, Austri, and Vestri (from where we take the names, North, South, East and West. Finally, from Ymir's eyebrow they shaped Midgard, the realm of man. The maggots which swarmed in Ymir's flesh became the elves and dwarves.
Humans do not appear until much later when three of the Aesir find two pieces of wood and give them life.
In the Norse View of the Other world, we find nine worlds spread across the three realms. These worlds are held together by the world tree Ygdrassil, each of the . Below is a map of just one of the many views of the nine worlds according to Norse Mythology.
The Upper World
1 - Asgard – Home of the Aesir (Also includes Valhalla)
2 - Alfheim - Home of the Light Elves
The Earth (Midgardr)
3 - Muspellsheim - Laying in the south, this is the home of the primordial fire
4 - Vanaheim - Land of the Vanir
5 - Mannaheim- Land of the Humans
6 - Jotunheim - Land of the Giants
7 - Niflheim - laying in the north, this is the land of the primordial ice
The Lower World
8 - Svartálfaheimr - Land of the Dark Elves
9 - Helheim - Land of the Dead
We could also look briefly at one of the Celtic views of the Cosmos. In the Irish view of the other world, the three realms are divided into several sections. Here is a list of those sections.
The Upper World - Magh Mór (Great Plain)
Magh Findargat (Plain of White Silver)
Magh Mel (Plain of Delight)
Magh Ionganaidh (Plain of Wonders)
Sen Magh (Old Plain) - Origins and Wisdom
The Middle World - Mide (Middle world):
Oithear (East)
Dess (South)
Siar (West)
Thuaidh (North)
The Lower World - Tir Andomain (Underworld)
Tir na mBeo (Land of Eternal Life)
Tir na mBan (Land of Women)
Tir fo Thuinn (Land Under the Waves)
Tir na n'Og (Land of Youth)