Vanaheim, home of the Vanir pantheon, is a Realm in Ysgard, neighboring the realm of Asgard (home of the Aesir pantheon). Locations within Vanaheim include Folkvang, the Field of Folk, where Freya's hall of Sessrumnir is; Noatun, the realm of Njord, a shipyard on the sea on the side away from Asgard; and Ydalir, the realm of Uller.
The Vanir include Frey, Freya, Uller, Njord, Gullveig, Kvasir, and others who keep themselves hidden away from mortal knowledge. It is not as mountainous as Asgard; in fact, it's a bit like Tir na Og with its rolling hills and winding coasts. The inhabitants of Vanaheim are slightly less warlike than their counterparts in Asgard, preferring intellectual pursuits, but still fight one another frequently, engaging in set duels only to be reborn the following day.
Sources:
Planes of Chaos, The Book of Chaos, pages 120-121
On Hallowed Ground, page 140, page 143, page 149 (Uller's realm),
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