A very special thanks to Stephen Castle, a course director for the National Association of Underwater Instructors (NAUI), an instructor trainer for the Public Safety Diving Association (PSDA) and an instructor trainer for TDI. He owns AAI Neptune Divers, Las Vegas, and he is cavern/cave–certified. I am grateful for his technical assistance and advice. Also, I’m proud to say, he is my brother. Really, it is just so useful having an expert in the family. Any errors in the text are mine, all mine.