PicnamView - a free viewer program: PicnamView Introduction - Navigation
Navigating between images
To move to the next image in PicnamView, hit Enter or Spacebar. After the last picture in the directory, the program asks whether you want to move to the next directory. Press Enter or Space again to move to the first picture in the next directory.
The keyboard shortcuts Alt+Up Arrow and Alt+Down Arrow move between pictures in the current directory. If the focus is in the image list, you can also use the arrow keys normally.

Navigating between Folders
The Prev and Next buttons move to the previous and next folders. You can also use the keyboard shortcuts Alt+Right Arrow and Alt+Left Arrow.