Usually, a part page has something printed on the recto and a blank verso facing the chapter opening on the next recto. For a striking and dynamic effect, I will use a single photo on the front and back of the part page. I put the left half of the photo on the recto and the right half on the verso, so the entire photo is viewed as the page is turned. Here are several examples:
When the reader encounters the part page (top spread), it looks like a routine tunnel. But when the page is turned, the two small workers in the lower left reveal the vast scale of the tunnel. That is a dramatic transition to the following section.
In another example, I used two similar photos of the same building for two editions of the same book. in fact in the earlier version, I used the architectural renderings and in the second, photos of the actual building.