The best replacement for cave is cavern.

The best alternatives to cave are rated as following:
★★★★★  cavern
★★  jewel cave
★★  wind cave
★  matrix
★  descent
★  cave
★  banal
★  igloo
  touhou
  dead cave
  grotto
  carlsbad
  carlsbad caverns
  blue cave
  diamond caverns

Your alternative for cave is not listed? Suggest!
Speaking about cave, one probably shouldn't forget about waterfall.

Other search terms related to cave and their ratings are:
★★★★★ waterfall
You have in mind a companion for cave and it is not yet here? Propose!



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cave
cavern
jewel cave