The castle in Gaujiena (Adsel) was created in an isolated enclave of the Teutonic Knights at the central part of the eastern border of Livonia, between the territory of the Archbishopric of Riga from the south and west, and the Duchy of Dorpat from the north. It was one of the oldest order castles in Livonia, because it was established between 1236 and 1238 on the site of a pagan hillfort, captured earlier by the crusaders. Due to its conventual shape, it is assumed that it was to be the seat of the commandry, but if it was so, it lost its function already in the mid-fourteenth century in favor of the castle Marienburg. In the hands of the Teutonic Knights, Adsel remained until 1558, when it was captured by the army of Ivan the Terrible. During the Livonian War, the castle changed owners several times, and about 1560 suffered serious damages. Reconstruction was carried out after subordination of the majority of Livonia to the Polish-Lithuanian state, thanks to which it retained its military significance and participated in the Polish-Swedish wars from the beginning of the 17th century. In the twenties of that century, the Swedes took it, and in 1702 it was finally destroyed by the army of Peter the Great. It has been in ruin since then.
The stronghold consisted of an outer bailey and a main castle measuring 29×27 meters, which owned surrounded by buildings, an internal courtyard of almost square shape and dimensions of 11×9 meters. The 2,8 meter wide gate led across the north-east wall. To the south of the upper castle stretched a wide zone of zwinger with a single bend and with a four-sided tower strengthening the outer wall. The northern ward was protected by another tower with a semi-circular plan. It was 12,4 meters wide and over 16 meters high, and its interior was covered by a stellar vault.
The fragment of the upper castle, a smaller fragment with a gate, relics of the north-western tower on the outer bailey and minor remains of the buildings have survived to this day. The area of the castle is heavily overgrown with trees and bushes, the admission is free.
Borowski T, Miasta, zamki i klasztory, Inflanty, Warszawa 2010.