Deep within the crypt, you'll find a large chamber with three glowing runes on the floor. To activate them, you need to find three 'Soul Gems' scattered throughout the surrounding areas. Each Soul Gem is typically guarded by a group of spectral enemies or a mini-boss. Follow the glowing trails that emanate from the runes to locate the gems. Once you pick up a Soul Gem, return to the chamber and place it on its corresponding rune. After all three are activated, a hidden passage will open, leading you deeper into the crypt and towards the chapter's boss.
