Object art by Andres Sanabria Guillen
Background art by David Nyari.
If you are the active player and an opponent casts a Spell while a Counterspell is in the discard pile, you may destroy Dark Altar to take the Counterspell from the discard pile, put it in your hand, and then play it to cancel the opponent's Spell.
This card has a few purposes. Other than being able to add 2 Cleric treasures to a dungeon, it allows the player to destroy this room (which can activate Recycling Center or activate an uncover room) to get another room card (like Bottomless Pit, which is always bound to be in the discard pile after being used) or a Spell Card that has been used for either the player, or an opponent.
"In the training grounds of Arcadia's most holy orders, no other room is discussed with as much fervor as the fabled Dark Alter. Legend has it that a dark hero known as the Demigod was born of this alter by the sacrifice of a holy paladin by Xyzax, the Progenitor Lich. Made a powerful beyond imagining by those dark magics, the Demigod escaped his dark lord and vowed revenge on all the masters of Arcadia's dungeons. Or so the story goes..."
-Excerpt from the Strategy Guide
""I love the smell of human sacrifice in the morning!" Yes, nothing like waking up in your Boss Monster crib and shuffling your fetid mass down to the Dark Altar to see who got sacrificed while you were snoozing."
-Excerpt from the Dark Altar card of the day entry
The glphs on the altar seems to be depiction of the All Seeing Eye room card.