Yggdrasil and the World Trees

The first World Tree, Yggdrasil, is the seat of wisdom and a connecting element between Midgard, Valhalla, and all other planes. Wotan and the Northern gods hold the secrets of how to travel its twisting paths and how to evade its guardians. Yggdrasil is ancient and perhaps sentient; certain of its trails are easier to follow than others. Those who travel Yggdrasil between the worlds carry messages for the gods or bring omens and warnings from Wotan and Loki.
The druids and elves agree that the Vanir elves—or Freyr and Freya themselves—planted the first seeds of Yggdrasil, which became the world and its many planes. Elven versions of this story say that Yggdrasil rests in the Summer Lands, and its roots and branches extend to Midgard, the Hells, and elsewhere. The druids and priests of Freyr and Freya claim Yggdrasil holds up Midgard and its offshoots form sacred groves and forests in the world.
The branches of Yggdrasil that enter Midgard manifest as World Trees that connect Midgard to various realms, from the Elflands to the Plane of Spears. Climbing a World Tree means entering the planar highways, which might lead to Valhalla, the Eleven Hells, or Ravatet. Only the elves, the ravenfolk, and valkyries even pretend to understand the paths, though the strange ratatosk native to the great tree act as guides, messengers, and guardians of its many planar roads.
The World Trees display roots as large as hills, and trunks pushing miles into the sky. Each tree’s bark is wildly variable, with sections of beech-smooth bark alternating with convoluted layers of flaking material. Their leaves are enormous, yet when they fall they seem to rarely reach the ground, instead slipping though the worlds to Valhalla or Elfheim or elsewhere.
The known World Trees are all sites of pilgrimage for followers of the Northern gods, but they are revered almost everywhere they grow. Each such tree is a node of divine power and is a nemeton, a sacred grove where no birds nest and no animals dig their burrows. The leaves of each World Tree constantly shiver and whisper, even when no wind stirs the forest around them.Druids and Northlands pantheon priests find their magic operates as if they were 1 level higher when they are within the sacred grounds of a World Tree.
The known World Trees include an enormous fir in Domovogrod; an unusual tree in Beldestan; a marsh cypress in the Haunted Lands of the Giants; a mere sapling in Huldramose; and a thriving ravenfolk roost in Trollheim. Not all World Trees prosper or resist corruption: Varshava’s tree did not survive the darakhul conquest of the city; the gnomes of Niemheim have created a terrible sproutling abomination; and a rotting World Tree endures in the ruins of Thorn.