Instructions
Make your way to Eterna City. Talk to the Underground Man at the southern part of the city in front of the entrance to the mines. He will give you an "Explorer's Kit."
Select the "Explorer's Kit" from the "Items" menu and press "start" to travel to the Sinnoh Underground. The Sinnoh Underground is a vast collection of tunnels to explore.
Locate any shining spots on the map. Travel to the shining spots and touch the DS screen to activate the digging mini-game.
Touch the rocks on the bottom screen of the DS to begin excavating. The top of the screen will tell you how many hits you have left. Use the hits to unearth fossils, spheres and evolutionary stones. Once the hits run out, the mini-game ends whether you have unearthed any items or not. You can find a limitless supply of evolutionary stones. But be warned that it may take some time because the stones are very uncommon in the mini-game.