#AdventuresInHistory!
#OTD #TDIH #September9, 1972 #MammothCave discovered to be world's #LongestCave.
#MammothCaveNationalPark #WorldHeritageSites #BiosphereReserves #LongestCaves #Caves #EdmonsonCounty #Kentucky #UndergroundSky
en.wikipedia.org/wiki/Mammoth...