get spheres and talk to a hiker underground
No you do not need wifi to go into the underground tunnles but you can use ds to ds action and play with your friends in the underground and trade and stuff.
nowhere
To get any stone in Dimand/Pearl you have to dig underground for it. You can also find some in caves and stuff like that i think.
The underground started in diamond and pearl so there is no underground in crystal.
Underground
underground
in the underground
lost towerfloor2 and underground rare in underground
If you mean the evolve stones then you can get them underground by using the explorer kit which can be found in eterna city by talking to the underground man. You have to dig in the walls to find stuff. The longer you spend down there the better the prizes are.
in the underground.
at the underground mine
underground...