Urban historian and explorer Steve Duncan has blown our minds a few times now via his incredible and ongoing urban exploration project, Undercity.

A serious-minded explorer not only of unused, forgotten, and ignored spaces in the modern metropolis, Duncan is also fascinated by the ways our cities absorb and transform natural waterways, diverting rivers and streams into subterranean tunnels and sewers.

Thanks to over a decade of exploring - much of it spent deep below his hometown of NYC - and a keen photographic eye, Duncan has become one of the most knowledgeable ambassadors for urban exploration. His photographs from deep below (and high above) New York and London offer an interesting comparison of these two metropolises. Both sets of images feature similar structures but the differences in age between the cities not only changes the visual feel of his photographs, but highlight how these two places developed over time.

To learn more, have a look at recent articles in the Daily Mail UK, and the Huffington Post.

A few of our favorite shots are below:

New York City

London