There are several ways to find the originals... but if you don't want to use Photos app, the easiest way is to select all the photos in the photos app (Command + A), then drag them to a folder on the desktop.
If you really want to do it the hard way, you can right-click (or Control-click) on the Photos database file called photos.photoslibrary which is usually stored in your ~/Pictures folder, select Show Package Contents then go into the "Masters" folder. There you will find your original, unedited photos.