Gemstone Caverns is a rare Legendary Land card from The List (PLST), collector number TSP-274. Current market price: $64.80, TCGplayer market prices via Scryfall.
If this card is in your opening hand and you're not the starting player, you may begin the game with Gemstone Caverns on the battlefield with a luck counter on it. If you do, exile a card from your hand. {T}: Add {C}. If Gemstone Caverns has a luck counter on it, instead add one mana of any color.