Related by context. Frequent words. (Click for all words.) 70 underground caverns 70 cavern 63 caves 57 subterranean 55 geologic formations 53 stalactites 52 salt caverns 51 rock formations 51 geological formations 51 cave 50 passageways 49 underground tunnels 48 stalagmites 47 tunnels 47 crypts 47 Caverns 46 grottos 46 dungeon 46 mine shafts 46 cellars 45 lagoons 45 dungeons 44 catacombs 44 Caves 44 burrows 44 labyrinths 43 underground 43 waterfalls 43 crevasses 43 limestone quarry 43 crevices 43 creatures 42 grottoes 42 limestone 41 orbs 41 Cave 41 ledges 41 quarries 41 vats 41 landforms 41 Cavern 41 Mammoth Cave 41 gullies 41 swamps 41 alcoves 40 reservoirs 40 streambeds 40 domes 40 aquifers 40 grotto 40 tunnels dug 40 ventilation shafts 40 hollows 40 mythical creatures 40 ancient tombs 39 ponds 39 wormholes 39 passageway 39 nooks 39 treasure chests 39 sandstone 39 cathedrals 39 shale formations 39 Egyptian pyramids 39 basins 39 rocky outcrops 38 reservoir 38 labyrinth 38 dank 38 crags 38 underground bunkers 38 valleys 38 coal seams 38 lava 38 unmapped 38 cavernous 38 bowels 38 root cellar 38 microscopic organisms 38 lakes 38 depths 38 cliffs 38 canyon 37 cosmos 37 cloisters 37 canals 37 petroglyphs 37 Saturn moons 37 staircases 37 castles 37 glacial lakes 37 blobs 37 casks 37 canyons 37 dome 37 spelunking 37 cellar 37 rocky cliffs 37 glens 37 sheer cliffs 36 sinkholes