Humidity is relative.
I am aware of some people living in Caves that have very low humidity levels.
Others, in the same area, have "plastered" the walls to stop the water seepage and reduce the humidity.
In Tenerife, the one I had contact with, his cave, mostly man made, had low humidity, he built it during a five years cycle, working few hours a week, until he acquired a small air driven equipment that allowed him to quadruple his work and end up with a beautiful cave setting, I wish his photos were at my reach to display them.
He found a small water spring when he was finishing one of the rooms, so he even had available clear fresh water, around 400 liters a day.
He placed roof rods and roof covering to stop possible drops and in addition re-enforcing some of the areas, just to be safe during nature up/downs.
He brought light via 500 mm light pipes and intake light concentrators, and regulated the internal temperature with outside filtered variable air, sometimes too cold for his family liking.
Beautiful cave arrangement.
Nando