The Abandoned Mine (廃坑 Haikō) is a small location in The Legend of Heroes: Trails in the Sky. It holds a boss fight when first entered and the dungeon itself has very little steps to get to into the area where the boss is fought.
After Schera, Joshua, and Estelle got info from the kid in Ravennue Village about 2 flying shadows heading to the Abandoned MIne, the group head to the mine with the key. Inside they find Kevin Capua and the other sky bandits along with the Linde next to them. Both sides have a brawl which ends in the Sky Bandit's defeat but they escape before they get captured.
After the battle, the group investigate the airliner but not before they leave that the Royal Army headed by General Morgan comes in and arrests everybody for meddling in Royal Army affairs.