Everyone else is talking about Apple, but I thought you were talking about Windows, because I had the same problem: the Metro Photos app likes to store things in AppData\Local\Packages\Microsoft.Windows.Photos_8wekyb3d8bbwe (!)
> the Metro Photos app likes to store things in (AppData)
I think that might be a bug. Windows 10 Photos app is surprisingly good about exposing your file system nicely, without the jank of a 'private proprietary hidden library' that other photo apps sometimes use.
Right click any photo to "Show in File Explorer" directly, or click Settings and it will show you a list of "Source Folders" it scans for pictures. Double click any "Source Folder" to jump straight into it.
At least, that's all present in the current version of Photos (2018 v18081.14710)
