“ Underground here, it's said that there's a legendary place where treasures were stored. ”
—Miner in the Underground Maze
Underground Treasure (夢？ 幻？ 宝物庫を探せ, Yume? Maboroshi? Homotsugura o Sagase, lit. Dream? Vision? Look for the Treasure House) is an event in Tomba!.
Find the legendary treasure in the Underground Maze.
Activate the event by walking though the door that needs the Unbreakable Wire from the event with the same name and talk to the miner inside. He will mention a treasure hidden in the Underground Maze.
Now, make your way up to the northernmost part of the maze, on the road to the hut of the Million Year Old Man, where a Million Year Old Treasure Chest can be found. Open it to obtain 300,000 AP and clear the event.