The caves are about five million years old and were formed by rainwater seeping through the cracks and fissures in the rock, eroding the layers below to produce cavities and hollow channels. Over a long period the cavities got larger creating enormous chambers. The dripping water also formed stalactites and stalagmites.
The Caves of Nerja are one of the top tourist sites in Spain. Concerts are often held there because of the good acoustics.