The first time many people ever put their head underwater is while snorkeling on vacation. With no certification or complicated equipment required, it’s a relatively easy point of entry for those who are interested in the marine world.  Because you only need a mask, snorkel, and fins, snorkeling is quite simple in theory. In practice, though, it's easy to have an unpleasant time if your mask keeps leaking, your snorkel fills with water every time a small wave rolls...