actually, i hit the cobble.
its becuase the stone around the dungeons are lined with cobble stone.
the normal cobble is smooth stone. that is how i know that i hit the dungeon.
so i found the dungeon
remember the coordinates.
i died, then i went back
i noted the coordinates before hand on my laptop.
i went and mined back.
hit smooth stone. then cobble was right next to me.
and usually, cobble doesnt generate naturally. that is how i know that i hit my dungeon was looking for.
so i mined 2 forward because i hit cobble.