Coastal caves are, by definition, caves that form along the coast as a result of the interaction of terrestrial and marine processes. Sea level can fluctuate, both globally as well as locally, and therefore the site of coastal cave development changes through time. Coastal caves form for two main reasons. First, wave and salt attack on any rocky coast can excavate simple hollows and chambers, called sea caves or littoral caves, in a variety of rock materials. Second, on limestone coasts, the dissolution of the rock by the mixing of freshwater and seawater can create complex cave systems called flank margin caves. Blue holes also form in limestone coastal regions from a variety of processes. Safe cave exploration in any environment requires training and preparation; while flank margin caves are relatively safe, the exploration of sea caves and blue holes can be extremely dangerous, even for those with years of experience.