How do u find somebody else's secret base underground in pokemon diamond??

Question

I just had a sudden intrest in pokemon so thats y i got this in 2008 not 2007 if anyone wants to know.please please somebody answer this question

Answer 1

you have to have another person next to you or close to that has either diamond or pearl. Then go underground with your friend and then on the bottom screen, it will have a blinking yellow square. It will show you were your friend's base is.