Dromar's Cavern

To keep this tri-land on the battlefield, you send a non-Lair land back to hand, paying a full turn of tempo for the privilege of fixing white, blue, and black off a single source. That is the Lair cycle's central trade, and Dromar's Cavern covers the allied combination later branded Esper. The design logic is honest about its cost: bouncing a land that has already tapped for the turn softens the blow, so the friction lands hardest when you have no spare to give and the Cavern simply dies on arrival. What keeps the trade from being purely punitive is that the returned land can be replayed, which means the Lair can reset a land carrying an enters-the-battlefield trigger or recover one you would otherwise be stuck with. Each of the five Lairs covers one allied three-color grouping, and they offered accessible multicolor fixing in an early era before triomes and shocklands made three-color manabases cheap and painless. The Cavern takes its name from Dromar, the dragon legend tied to this slice of the color pie, so the land reads as a piece of faction worldbuilding as much as a fixing tool: the Lair is literally the dragon's home, and you pay rent in tempo to occupy it.