The Sacred Ground Ruins are a location in The Legend of Zelda: Breath of the Wild. The ruins are located in front of Hyrule Castle in the Hyrule Field region. The area is quite dangerous due to the number of Guardians in and around the ruins. It is the place of the first lost memory, "Subdued Ceremony", during the main quest "Captured Memories".
The Master Trials
Upon "The Master Trials" DLC pack installation and during the side quest "EX Treasure: Phantasma", Link can dig up a Treasure Chest containing the Phantom Armor and buried in the southeast of the Sacred Ground Ruins, by using the Magnesis Rune.