The Akkala Citadel Ruins are a location from The Legend of Zelda: Breath of the Wild. They are located in the Akkala Highlands region of Hyrule. It is the ruins of a citadel that was once located in the Akkala Highlands which played an important military role during the Great Calamity and Age of Burning Fields. In the middle of the Citadel Ruins, Link can find the Akkala Tower which contains the Sheikah Slate map data for the Akkala region.
Background & History
The Akkala Citadel was apparently a formidable military fortress during its heyday one hundred years ago and seems to have been important military facility as it features a parade ground and contains several artillery batteries for defense, indicating that it likely played a key role for Hyrule's military as it is the second most imposing fortification in Hyrule after the kingdom's capital Hyrule Castle and Hyrule Castle Town. Though its purpose before the Great Calamity is unclear, its location in Akkala implies that it may have been a military base to defend the entire region as well as a location to mobilize and serve Hyrule's armies in the event of war, and potentially as a fall back point should Hyrule Castle be destroyed or fall as it has several times in the past. It is implied that the Citadel was built over the buried Akkala Tower as it is implied part of the ruins where the result of it raising from the ground after Link activated the Great Plateau Tower, causing other towers to spring up all over Hyrule. Thus it is possible that it was built to protect the towers location though it is more likely was unknowingly built over it as the fortress is implied to have suffered damage from its raising out of the ground. Regardless, the fortress is one of the most technologically advanced military structures in Hyrule not derived from ancient Sheikah technology, as it is equipped with cannon batteries, that would presumably make attacking it foolish for any monsters or conventional army without access to similar artillery or advanced ancient Sheikah technology and armaments.
Fall of Hyrule & Last Stand to Ruin
After the fall of Hyrule Castle to Calamity Ganon during the Great Calamity event, one hundred years ago, the surviving Knights of Hyrule and Hyrulean Soldiers fell back to the Akkala Citadel. However they where soon attacked by Guardians and monsters loyal to Calamity Ganon during the Age of Burning Fields. This place was where the Knights and Soldiers valiantly made their last stand against Calamity Ganon's forces, but in the end were slaughtered and utterly annihilated. It is implied that all the remaining Knights of Hyrule were killed, leaving Link the only surviving member of the order. Most of the Hylian Soldiers died though it is revealed that at least one managed to leave behind a descendant indicating the possibility that others did as well. However no remains can be found with the exception of their weapons and soldier armor which it is implied was salvage by the surviving people of Hyrule and made its way into armor shops such as Ventest Clothing Boutique in Hateno Village which managed to conserve it to be sold to travelers and potential by mercenary soldiers for hire such as Hoz for protection. Meanwhile the monsters and people are implied to have looted any surviving intact armaments wielded by Soldiers and Knights of Hyrule, leaving only rusted out weapons and shields. Over time the citadel's cannon batteries became derelict and inoperable.
A century later, Link can find a Hylian traveler named Nell fighting with a Moblin on the Akkala Bridge Ruins leading to the citadel. Link can assist him by defeating the Moblin and Neil will reward him with Rupees or a random dish or elixir. Neil reveals the history of the Citadel and its role during the Great Calamity. Neil made a pilgrimage to the citadel to honor a Hyrulean Soldier ancestor, but was unable to reach it due to the broken bridge and the patrolling Guardian Skywatchers. The ruins near the tower show signs that indicate they may have been damaged when the Akkala Tower rose from the ground, though it is unclear if they where present before the tower rose up or not. Pools of Malice surround the tower, forcing Link to destroy Glowing Eyeballs and Magnesis Rune to create paths. He also has to contend with monsters and Guardian Skywatchers stationed the ruins. Several Guardians litter Torin Wetland to the east of the Citadel, implying they where taken out during Citadel's last stand, either by soldiers, knights, and/or by a concentrated artillery barrage from the Citadel's cannons as Guardians can be defeated using lower tech medieval weaponry such as swords, bows, and shields with a well-timed Perfect Guard so it is possible the cannons where powerful enough to take out at least some of them as part of a well coordinated defensive assault. However ultimately it is implied that like Link before them, they were outnumbered and overrun by the Guardians, though unlike the Hylian Champion where killed by the corrupted ancient automata. However the Citadel ruins, its rusted out inoperable cannons and Guardian remains stand as silent reminders of the battle that took place here.