Nidavellir is the home of the Dwarves, and one of their main activities is to serve as blacksmiths. As such, Nidavellir presents some of the best forges in the Nine Realms. It was here where they created the hammer Mjølnir.
In a plot to overthrow Odin as king of Asgard, the Asgardian Imir invaded Nidavellir, and barricaded himself in the Golden Forge. There, he took the Dwarven Smiths as hostages and made them forge an Axe capable of cutting through the fabric of reality.
When Thor arrived to Nidavellir, he confronted Imir, but he was taken by surprise by the powers of Imir's Axe, that allowed him to open small portals and teleport himself through the room, catching Thor off-guard until he was able to summon lightning through the chimney of the forge, electrocuting Imir and liberating the Dwarves.
When the Bifrost Bridge was destroyed, the Rock Trolls, having coveted the Dwarven Forges for many millenia, attacked Nidavellir, knowing that Asgard could not come to defend King Eitri and his people.