| Category | Volcanoes |
| Region | Necrocrypt |
| Location | Gathrot |
| Map | Nithlurik |
Gruggvein is an active volcano situated in the northern region of Gathrot. It is not a natural geological formation, but rather a product of the divine intervention of a god. During the God Era, Surtur became the progenitor of fiery terrors known as the phaethon. These fearsome progeny of Surtur were wild and untamed, driven to set everything ablaze. Aware of the potential consequences, Surtur imprisoned a few of these entities within the seabed of the Sea of Mourning. Through divine compulsion, the phaethon were willed to remain semi-dormant and permanently in place. Despite their constrained state, their semi-dormant existence allows them to influence the surrounding area. Surtur entombed at least two phaethon beneath the Sea of Mourning, with the two located in the region of Necrocrypt, an island landmass they created, being named Gruggvein and Groarnfer. These two active volcanoes of Gathrot's central island are named after Surtur's fiery offspring.
Gruggvein is the more active of the two volcanoes of Gathrot. This is because the lava tubes of Groarnfer were redirected northward to Gruggvein. This seemingly divine undertaking was carried out by an army of magmin, summoned to this realm by a crazed undead lord named Dax. He dubbed this project the Groarnfer Plan. It entailed redirecting lava tubes and pressure from the southern volcano to the northern volcano, all in an effort to save Satheon. The Groarnfer Plan was vast in scale, yet the potential wealth of Durkoth relics in undersea ruins was sufficient to justify the task, at least in Dax's mind.
When the Groarnfer Plan was completed, Gruggvein began to erupt more frequently and violently. After a few years of managing thousands of mischievous and bored magmin, Dax and his overseeing Dao put them to work on the Gruggvein Plan. This plan, even broader in scope than the first, aims to expand the landmass of Gathrot. Rather than a haphazard approach, the dao are guiding the magmin's efforts to direct the lava along sea ridges, enabling it to join the islands traveling westward towards the Buccaneer Archipelago.
Most of Gruggvein's eruptions spill into the volcanic wastelands of Girzinnuk. Within this region, the majority of the lava traverses magmin-constructed canals that extend northward and northwestward.
Gruggvein, akin to its sibling volcano Groarnfer, is intricately riddled with thousands of chambers and passages. These provide entry to the lava tubes of the volcano and function as barracks for the magmin, forge areas, and additional general-purpose zones.
In the farthest recesses of Gruggvein, the magmin laborers unearthed a smoldering stone engraved with archaic inscriptions:
Gruggvein, the wayward and untamed progeny of the flames, shall now find eternal respite.
from the Burning Stone of Gruggvein
Research on the matter has culminated in the theory that this Igneous Monolith was strategically positioned by Surtur, and beyond it lies the repository where his son Gruggvein is sequestered.