Instructions
Press "X" to access the menu and select "Bag."
Select "Key Items" followed by "Explorer Kit."
Select "Use" followed by "Yes." You are taken into the Sinnoh Underground.
Explore the Underground until a yellow blinking light appears on the map on the top screen of your Nintendo DS. The location of the light is random and indicates there is treasure in that location.
Tap the touch screen when you are in the location of the yellow blinking light. Small white lights appear on the walls of the Underground.
Press "A" while standing next to one of the white lights and select "Yes" to begin digging.
Use the hammer and the pickaxe to unveil sections of the wall to search for items. Items are shown as colored stones hidden inside the wall in random locations. Every hit of the hammer or pickaxe causes the crack at the top of the screen to lengthen. When the crack reaches the other side of the screen, the wall collapses and all unfound items are lost. However, you keep all items you find before the wall collapses.
Press "X" to access the underground menu. Items found are placed under the "Goods" and "Treasures" submenus and can be transferred to your bag.
Exit the Underground by selecting "Go Up" from the menu.