At first sight, this seems like a propeller about to get attached to an airplane engine. I thought the same until I looked closer. Then it blew my mind. Zoom in and discover why.

Can you see them? Look in the holes. There are workers inside that turbine. Not little people, but full-scale humans. So no, it's not an airplane propeller: It's gigantic propeller waiting to be mounted on power windmill turbine by people working from inside the turbine itself.

The windmill is one of the two currently being installed in the city of Hamburg, Germany, and it's officially rated at 6 megawatts of power. Not enough to travel in time, but amazingly cool anyway.

And you thought the one that required an helicopter to reach its top was big. [Big Picture celebrates Earth Day—Thanks reader Faiz for the wider shot]

Send an email to Jesus Diaz, the author of this post, at jesus@gizmodo.com.