Landvættir (land spirits) are mythical creatures in old Icelandic literature and stories. They are chthonic guardians of specific grounds, such as wild places.
Landvættir can shapeshift into troll-animals endowed with magic power and super strength.
The biggest of them dwelled in four places in Iceland: a dragon in Vopnafjörður, the bird in Eyjafjörður, the bull in Breiðafjörður and the giant in the south.
Landnámabók tells of a time when King Haraldr Gormsson, King of the Danes, intending to invade Iceland, orders a wizard to travel to Iceland and tell him of what he sees there. The wizard goes in the form of a whale, and goes west of the north of Iceland. There he sees that all mountains and hills are full of landvættir, some big, and others small.
When he comes to Vopnafjörður he tries to walk on land, but is thwarted by a great dragon who is followed by many worms, bugs and lizards who breath poison on him. So the wizard tries to go to the west, to Eyjafjörður.
There he is met by a bird, with wings so long that they touch the mountains to each side of the fjord, along with many other birds. The Wizard continues west and south to Breiðafjörður and heads to land where he meets a giant Bull who wades into the sea and bellows at him mightily, followed by many landvættir. The wizard goes south around Reykjanes and tries to swim ashore on Vikarskeiði.
There he met with a stone giant armed with a staff of iron, taller than the mountains and with many jötnar following him. Next the wizard tries to go to the east. There he sees nothing but sands and wastelands with tall waves crashing its shores, where long ships cannot land.