Castle Garenbrig is a rare Land card from Throne of Eldraine Promos (PELD), collector number 240p. Current market price: $9.13 (foil $8.36), TCGplayer market prices via Scryfall.
This land enters tapped unless you control a Forest. {T}: Add {G}. {2}{G}{G}, {T}: Add six {G}. Spend this mana only to cast creature spells or activate abilities of creatures.