Rocks like fangs, secret lakes, hidden ponds. We explored a long, deep cave in the woods a few miles from where my parents live. In pre-Roman times, the cave’s main room, at the foot of the mother rock, was a temple to pagan gods—the local people left offerings shaped like tiny boats just above one of the subterranean ponds. But the essence of the cave remained hidden until relatively recently, when some local miners enlarged a natural passageway on one side of the main room. What they saw took their breath away—and ours. Miles and miles of deep chasms and soaring columns, veils of candid limestone and depths of sapphire waters. The place is called Su Mannau, near Iglesias, in Sardinia. If you are ever there, it is well worth a visit.