"Mysterious caves" refers to hidden or unknown underground spaces that provoke curiosity or a sense of wonder due to their unknown or secret nature. Full definition
Explore, survive, and ultimately build a resource - intensive spacecraft to escape the dangers and mysterious caves of this circular world. (indiemegabooth.com)
After zip lining we got a chance to take it easy by cave tubing in the dark mysterious cave, where we saw and learned a lot about limestone formations. (splashbelize.com)
Explore sandy beaches and majestic forests; investigate mysterious caves or paddle down peaceful rivers — an adventure awaits every visitor. (env.gov.bc.ca)