Some think that the carved dragons on its ramparts are actually petrified dragons because they are so lifelike. Davos alludes to this.
I may be thinking of the exact POv, but I recall the text describing the sculptures throughout the castle (which is much more massive than the show lets on, the pic a few posts ago more accurate, IMO) actually transverse halls/ rooms, and if you singled out any one dragon, you might see the head and neck from the exterior, and the back/wings on the interior...or vice versa; none are disembodied heads, but all are complete, body and all...as if the castle itself were made of intertwined dragons...seems like he tried to count them once and lost track after a Rediculous number.
It was obvious to me they were all actual dragons waiting to be released...unless this was the idea behind the structure itself, to make would be invaders think twice, or just homage to the prophecy of AA in architecture. Hell, dragonstone may not be as old as say, Winterfell, but we know its older than the Doom.
I don't remember the active volcano on dragon stone, biut that would explain the black beach rocks...