Gemstone Caverns is a mythic Legendary Land card from Time Spiral Remastered (TSR), collector number 280. Current market price: $59.99 (foil $114.77), 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.