One of the six horns, built into the foot of the Long Reach. Ridgehorn looks out over Denglr's Bay and Strand, built at the time when dredge regularly emerged from the deep fjords nearby, threatening commerce. Over time the dredge diminished near Ridgehorn, then stopped altogether, the fort falling to disuse.
In actual, Ridgehorn along with other fortresses with the suffix "horn" in their name is a portal to the dredge homeworld built by the menders.
The region surrounding Ridgehorn had become infested with bandits shortly before the Dredge arose again.
The Valka Eyvind after performing the ritual to resurrect Juno, fled back through the portal but was confronted by a force of the Dredge. He however was able to kill all of them using his powers, losing consciousness in the process and damaging the tower.
During the events of Banner Saga, the party of Varls and humans led by Hakon decides to travel to Grofheim by way of Ridgehorn. While journeying to the place, they witnessed the lighting, utlised by Eyvind agaunst the Dredge.
Hakon's party had no idea though what had happened. When they reached the fort, they found littered corpses of the Dredge, not knowing what had happened.
They also found Eyvind and Juno on top of the tower. Since Eyvind was still alive and Juno not yet resurrected, they decided to take him along after being suddenly confronted by the Dredge. Battling their way through, they managed to escape the fort.
In Banner Saga 3, Iver and his party visited the fort. There, Iver was informed by Juno and Eyvind of the tower's true purpose - a portal to the Dredge homeworld that existed underground.