Default Gallery Type Template

This is the default gallery type template, located in:
/var/www/vhosts/hoeden-atelier.nl/httpdocs/hoeden/wp-content/plugins/nextgen-gallery/products/photocrati_nextgen/modules/nextgen_gallery_display/templates/index.php.

If you're seeing this, it's because the gallery type you selected has not provided a template of it's own.