The biggest open mine in the world is located in Russia in the town called Mirniy. It’s somewhere in Siberia if you don’t know. Basically, it is a huge hole in the ground, which is about 600 meters deep and has an opening diameter of 1200 meters. It doesn’t sound as big as it looks on the pictures though. Check the pictures here and here (one, two, three, four, five, six).
There is no way you won’t say “Wow!”.