There are secret underground military bases in Spain?

Hi all, I wanted to know if any of you know if there is any underground military facility under Spain. There are speculations that there about underground bases around the world, but it is also possible that there are in Spain?

As a matter of fact, secret CIA flights have landed in the naval bases of the Spanish army, and I wonder if there might be some inside connection that does not yet know. If anyone knows anything please, give me some source to research further. Thank you.

greetings.