.APALBUM File Extension
What is an APALBUM file?
Photo album created by Aperture, Apple's commercial digital photo editing application; saves an album of imported photos, which can be part of a larger Aperture project; usually has a cryptic filename prefix since Aperture handles the image data using a proprietary format behind the scenes.
APALBUM files are not meant to be opened directly. Instead, they are opened using the album features in Aperture.
NOTE: Apple Aperture was discontinued and replaced by Photos in 2015.