Use the interactive seed-map finder on this page: enter your world seed and Java Edition version to see the exact coordinates of every Mineshaft. In-game, Mineshafts are underground, so dig down and explore cave systems (which they often intersect) until you spot wooden support beams and rails; in Badlands biomes the dark oak variant generates near the surface.
Mineshafts are an Overworld-only structure and can generate underground in nearly any biome. The standard variant uses oak wood and spawns deep beneath the surface, while Badlands (Mesa) biomes produce a unique dark oak variant that generates much higher up, sometimes exposed at or near the surface.
Mineshafts contain minecart-with-chest loot including rails, iron and gold ingots, name tags, lapis, and a rare enchanted golden apple. They are the only structure with Cave Spider spawners (hidden behind cobweb clusters), so bring a sword and torches before mining toward the corridors.
