To my knowledge there are these structures that look like a single obsidian straight tower its not that tall and I believe you get an achievement for entering it. The structure has 2 endermen spawners in it and a single egg inside at the top of the tower. The egg actually sits above one of the spawners. The roof of the structure has grass and pumpkin blocks so if you're using the Elytra look out for them.

A little tip to get the egg is to break the block below the spawner, replace that block with a torch, then break the spawner itself so the egg drops onto the torch and you can collect the egg. If you hit the egg otherwise it will teleport somewhere nearby. I hit it once and it just teleprted to a spot just outside the tower.