Spawn near a village with blacksmith at coordinates 280 296. Take a peek inside the smithy's chest, and grab all that obsidian for your powerful structures. Then, follow the path along the river in the southeastern direction.
Soon you will arrive at a huge woodland mansion at coordinates 500 600. The tall foundation allows for some secret rooms, one of which can be found at coordinates 487 71 597. Inside the room you will find an enchanted axe with Efficiency I.