Black durgon (triggerfish).Not long after we became official PADI open water divers, we signed up for the advanced open water course, basically one level up from being an open water diver, with the biggest benefit being the ability to dive up to like 100+ feet (the limit for open water divers is 60 feet).To become advanced open water divers, you have to complete five dives: a deep dive, underwater navigation and three “adventure dives” of your choice. Kail and I did our deep dive and natural navigation dive in Lago Ilopango, then completed our three adventure dives in Utila: shipwreck, night dive and fish ID.Natural navigation in the lake.The deep dive was kind of neat because we did a nitrogen narcosis test once we got to our depth — 118 feet! Nitrogen narcosis occurs while diving at depth, when concentrations of nitrogen in the body start to have an intoxicating effect. It sounds serious, but really it means you feel like you had a couple beers — not drunk, but buzzed (tocada, if you will). So it’s like, Hello, what’s the problem? Well, similar to the effects of alcohol, nitrogen narcosis can impair judgment and affect one’s decision-making, which when you are 100 feet below water, can be a bad thing.We did a simple test: We had to point to the numbers in the grid pictured below in order from 1 to 25. We did the test first on the boat and then once we got to depth, and compared the difference in time between the two. I went first; above water I counted the numbers in 24 seconds and underwater it took me 35 seconds. Kail went next; he took 32 seconds above water and 51 seconds below water. Another dive named Boris went last and he could not even complete the test underwater. That is how much of a difference even a couple minutes makes when you are underwater that deep.Nitrogen narcosis!Natural navigation did not go that well in the lake, where it is really hard to see. I mean, we swam for a while, turned around, and swam back, and when we surfaced we were somewhat near our boat. But I don’t know if that was just luck, or if we really knew where we were going (speaking for myself, I did not — I have a terrible sense of direction on land!).The coolest dive was the night dive we did in Utila. I admit I was mildly terrified, but it got dark so gradually that I didn’t even notice it was pitch black underwater until well into the dive. We had flashlights, but then at one point we all turned them off and were able to see all kinds of life glowing underwater. Fish ID class with David.Fish identification … not sure I have the hang of that yet either. We saw a million different kinds of fish in Utila and later went over them all, using pictures, but I’ll be honest: I do not remember most of them. Perhaps because our fish ID class was taking place during our rum celebration.Do you have a good sense of direction?