Sanctum of Calm Waters is a uncommon Legendary Enchantment — Shrine card from Core Set 2021 (M21), collector number 68. Current market price: $0.40 (foil $4.90), TCGplayer market prices via Scryfall.
At the beginning of your first main phase, you may draw X cards, where X is the number of Shrines you control. If you do, discard a card.