In Act 2, upon arriving at Moonrise Towers and conversing with the antagonists, you'll go into Balthazar’s room and activate a hidden book on the shelf revealing the Ancient Altar. The room is scattered with bodies, likely subjects of Balthazar’s experiments. You will need to solve the puzzle at this point.

What Goes In The Ancient Altar?

Retrieve a heart from one of the bodies and place it in the Ancient Altar. This will resolve the puzzle, unveiling a concealed passage behind the bookcase leading to Balthazar’s secret necromancy chamber. A severed head also works, as any body part found in the vicinity of the altar can activate it.

Location of the Ancient Altar: The Ancient Altar is located in the right side of Balthazar's Room, a notable location in the Act 2 Shadowlands of Baldur's Gate 3. Adjacent to a peculiar bookcase, this altar stands as a testament to the game's rich history and the mysteries it holds.

Function of the Ancient Altar: The primary function of the Ancient Altar is not immediately apparent. However, through exploration and interaction, players have deduced that it plays a role in various quests, especially those related to the Chosen of Shar and the Gauntlet of Shar.

Items for the Ancient Altar: The Ancient Altar requires specific items to activate its potential. One of the primary items identified is the Umbral Gem. Players need to collect three of these gems to interact successfully with the altar. These gems are scattered throughout the game and require keen observation and exploration to locate.

Associated Quests: Several quests in Baldur's Gate 3 are intertwined with the Ancient Altar. The Gauntlet of Shar quest, for instance, has direct ties to the altar. Players navigating this quest will find themselves returning to the altar multiple times, using it as a pivotal point in their journey.