Thosgeir is the southernmost tip of the Ognar fjord. The only reason this area is not frozen over is because of its proximity to a Temples of Begnhidrir. The heat of this temple's cauldron keeps the unnatural glacial flows of Ice Cap from moving into Begnhidrir and the lowlands beyond.
Thosgeir is not a true lake. It is really just a part of Ognar, with the surface of most of this fjord being frozen over. Ongar and Thosgeir are still linked by an underground channel. Above this channel are several hundred feet of ice and snow.
The presence of the Temple of Begnhidrir and the chilling air of Ice Cap results in a near perpetual pall of smoke and fog over the lake and the surrounding area. The conditions of the area are such that lichen and other vegetation thrive in the area's humid conditions. These conditions also suit the people of Hel who come here for swimming, hunting game, an collecting foodstuffs.