The pinhole camera uses the principle behind camera obscura in order to expose film and capture an image. Michael Wesely's work show varies scenes of city construction. Pinehole cameras historically have very long exposure times, and Michael's work is not much different.
Michael exposes the images between a few weeks to even a few years. Wow!
I have decided to make an edit because it seems everyone is interested in knowing more about this project!
It seems that my initial assumption that all of these photographs were pinhole photographs is in fact wrong. However, Wesely did use pinhole photography and some of these shots are pinhole photographs (I am just unsure of which exactly).
Wesely has worked on projects and books that focus on his unique style of photographing. He would often use filters and extremely small apertures to reduce the amount of light striking the film.
To address your point @cheerfulcallie, it is indeed possible to take pinhole photographs for days, weeks or even multiple years. One must use of an extremely small pinhole aperture (smaller than the size of a pinhead), this will limit the amount of light that can expose the paper. Also, the use of a very very very slow developing paper is the key. Wesely likely used paper of 5-10 ASA or slower (ASA = ISO).
Wesely spent decades perfecting this technique of extremely long camera exposures, using pinhole cameras and large format cameras. He said that this technique could be used for an exposure of 10, 20, or even 40 years!
@EnriqueHuerta I hope this additional information helps! :)