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Lyngvi is the island where the gods imprisoned Fenris Wolf.

It is described as looking like the crater of an extinct volcano in the sea and being covered in white heather flowers that helps keep Fenris Wolf imprisoned.

Magnus Chase and the Gods of Asgard

The Sword of Summer

Magnus Chase, Samirah al-Abbas, Hearthstone and Blitzen arrive on the island and check on Fenris Wolf. They are found by Gunilla, two other Valkyries and Magnus’s hall mates. The son of Frey’s hall mates join him and fight Surt when his forces arrive. The wolf is cut free and battled by Sam until he is rebounded by Jack and Magnus banishes Surt and his forces. With the Valkyries dead the remaining forces return to the Hotel Valhalla.

Locations (MC)
Nine Worlds: Alfheim | Asgard | Helheim | Jotunheim | Midgard | Muspellheim | Nidavellir | Niflheim | Vanaheim
Cities and Towns: Boston | Flåm | New London | Provincetown | York
Administrative Divisions: Connecticut | Massachusetts | New Hampshire | North Yorkshire | Sogn og Fjordane | South Carolina
Countries: Confederate States of America | Norway | United Kingdom (England) | United States of America
Continents: Europe | North America
Other Locations: Alderman Estate | Bifrost | Blitzen’s Best | Boston Public Library | Bridal Veil Falls | Cape Cod | Charles River | Charleston Harbor | Chase Mansion | Dorchester | Fadlan’s Falafel | Folkvanger | Fort Wagner | Ginnungagap | Hotel Valhalla | Loki’s Cavern | Longfellow Bridge | Lyngvi | Morris Island | Nabbi's Tavern | Provincetown Airport | River Oure | Sessrumnir | Svartalfheim | The Thinking Cup | Yggdrasil