Darksteel Citadel

Most lands settle for producing mana and getting out of the way. This one keeps mana in the picture while quietly refusing to leave: indestructibility on a colorless source means board wipes that catch lands, damage-based sweepers, and targeted land destruction all glance off it. The trade is real and printed into the rate: it taps for colorless only, so a deck running it accepts a worse mana base in exchange for a land that survives what kills everything else. That bargain made the most sense for builds where the artifact subtype mattered as much as the indestructibility. As an Artifact Land, it counts toward affinity, feeds metalcraft, and turns on every "you control an artifact" condition, all while sitting in the manabase rather than competing for a spell slot. The Mirrodin-block artifact-lands experiment is what put it on the map, and that lineage is also why so many of its siblings drew bans across formats: a land that is also an artifact bends the cost curve of any deck built to count permanents. Darksteel Citadel is the one that endured, partly because colorless mana is the least exploitable output and partly because indestructible, by itself, doesn't accelerate anything. It just refuses to die, which in the right shell is its own kind of acceleration.