Dark Ore Mine

Dark Ore Mine is a location in Spirit Tracks. Situated in the Fire Realm, it is inhabited by Gorons who mine the place for Dark Ore. Link can only access this station after he receives a Force Gem from Ferrus as a sign of gratitude for taking him to the Ocean Realm. Once this is done, the Force Gem will reveal Spirit Tracks to the mine. As mentioned by the Gorons, since Dark Ore disappears when exposed to sunlight, they must mine the ore while working in complete darkness so as to keep it in tact.

Here, Link can purchase ten pieces of Dark Ore for 200 Rupees, five of which he can take to Linebeck III in the Trading Post and receive a Force Gem from him to gain access to Lost at Sea Station in the Ocean Realm.

Trivia
Oddly enough, the Dark Ore Mine slightly resembles a Goron's face.