"This trapper outpost once snared and shipped dragons to Drago Bludvist’s army — until Valka's Bewilderbeast obliterated it. The fort’s frozen wreckage remains preserved in the ice blasts, serving as a warning to dragon trappers everywhere."
Eret's Fort was once a thriving outpost for trappers to trade and ship dragons to Drago, complete with docks for ships, cages to house captive dragons and weapons. There are even raised docks for archers to fire. But since the attack by Valka's Bewilderbeast, the fort was been reduced to splinters and ice spikes. Eret and his fellow trappers since reside there in the beginning of the second movie, ready to attack any dragon or rider that passes by.
Hiccup and Astrid noticed smoke from Itchy Armpit and went to investigate. They had unknowingly fell into the traps of the dragon trappers and Stormfly was caught. Eret makes his first appearance here and accused the duo of wrecking the fort. Luckily, Toothless blasted the ice spikes, making time for Hiccup and Astrid to free Stormfly.