I recently went to Cueva de los Verdes - last time was over 10 years ago!!
I had forgotten how narrow some of the tunnels / steps were!
The Official website states
"It came about after the eruption of the Volcán de la Corona, and it’s one of the most impressive hidden wonders in the depths of Lanzarote. It was used as a hideout by the locals who needed shelter to protect themselves from invasions and attacks of pirates coming from the north of Africa during the 16th and 17th Centuries. In the 19th Century, it became a must for travellers, experts and European scientists due to the uniqueness of this volcanic territory, named after a family that kept their cattle in the area!"
If you have not been, you need to go and there is a surprise at the end of the guided tour, I will not mention what it is, as that would spoil the surprise !