National Geographic : 2009 Jun
SUB SOLOMON CAVE TENNESSEE Dissolving layers of ancient limestone, moving water sculpts underground terrain. Cavers ready for a long shower enter 405- foot-deep Sub-Solomon at its base and climb up against the flow of four waterfalls, including this 65-footer. IRON HOOP CAVE ALABAMA Millennia in the making, fantastical chambers like this are decorated by the infinitely slow accumu- lation of minerals (chiefly calcite) deposited by water dripping through rock. Encounters with such rare and fragile beauty are highly prized.