a fortress of frozen breath that stays warm by trapping your own body heat
means a dome-shaped shelter built from blocks of compacted snow, traditionally used by some Inuit peoples for winter dwelling or hunting camps.
from From the Inuit word "iglu" (in the Inuktitut language), simply meaning "house" or "dwelling" — not specifically a snow house at all. To Inuit speakers, an iglu could be made of stone, sod, or skins; English borrowed the word in the 19th century and narrowed it to the famous snow dome. The word is a cousin of forms across the wider Eskimo-Aleut language family.
inuit snow houses greenland — traditional dome structures built by inuit peoples in arctic regions for winter shelter
igloo village switzerland — seasonal igloo hotel in valais that rebuilds each winter with real snow blocks