Nidavelir is the realm of the dwarves.
As Etrie and his two warriors fled to The Forge, they bumped into Iron Man and picked him up. After explaining to the mortal, they ran into Ulik. The battle was hard fought, two dwarven warriors were dead, leaving only Etrie and Iron Man victorious over the troll. After Ulik's defeat, they went to The Forge where they built the Thorbuster armor made from the metal uru and based on the Destroyer in preparation in his battle against Loki with the Avengers.
When Loki is defeated by the Avengers, all of the realms were free including Nidavelir.