Hall of Storm Giants is a rare Land card from Adventures in the Forgotten Realms (AFR), collector number 257. Current market price: $0.47 (foil $0.63), TCGplayer market prices via Scryfall.
If you control two or more other lands, this land enters tapped. {T}: Add {U}. {5}{U}: Until end of turn, this land becomes a 7/7 blue Giant creature with ward {3}. It's still a land. (Whenever it becomes the target of a spell or ability an opponent controls, counter it unless that player pays {3}.)