The Hyrule Garrison Ruins are a location from The Legend of Zelda: Breath of the Wild. It is located in the area southeast of the Central Tower and north of Windvane Meadow in the Hyrule Field region. It was the site of a garrison before the Great Calamity before becoming overrun by Guardian Stalkers. The Central Tower was buried where the Hyrule Garrison constructed. A Silver Rupee, an Opal, a Forest Dweller's Sword, a Royal Shield, and a Serpentine Spear can be found within Treasure Chests left behind in the ruins. Searching the Broken Guardians and destroyed carts found within the ruins may yield Amber, Flint, or random Ancient Materials.
The Master Trials
Upon "The Master Trials" DLC pack installation and during the side quest "EX Treasure: Phantasma", a Treasure Chest that contains the Phantom Greaves can be found buried in the southeast of the Hyrule Garrison Ruins.