it seems this master page does not exist in pages. and there’s not much of a choice to open those images somewhere else – it is either a viewer or attachment page. So even if I was to create new page or template I would not be able to change that option which is set there by default. PAGES/GALLERY edit, add media – Link thumbnails to: Image File or Attachment Page.
This is part of the way WordPress handles image attachments. By default, I believe they use the single.php template which you can edit in the theme files and the loop that it uses to output the post in includes>loop-index.php (though be careful as that loop is used by a lot of other templates as well).
According to the codex entry on hierarchy, it looks like you could create an image.php and that would then load up for images instead of using single.php so there is that option as well.