Today, after completing five specialty adventure dives with Summer Salt Dive Center in Playa del Coco, I proudly earned my PADI Advanced Certification. Yesterday we had experimented with shipwrecks and buoyancy, photography and night diving. There were only two dives left for today: deep and navigational.

The purpose of the deep dive is to demonstrate that the farther a person descends below the surface, the more likely they are to feel buzzed or high. This temporary lightheaded sensation is called nitrogen narcosis, also known as the ‘martini effect.’ It is a completely reversible symptom that can occur at profound depths, usually greater than 100 feet. For some, this feeling is not even noticeable; to others it is downright enjoyable. After all the hype, I was lucky enough – or unlucky enough, depending upon your point of view – not to feel anything at all.

In any case, it is important for divers to be aware that their reflexes are hampered at deep depths. To illustrate this point, we were asked to complete a simple mental exercise where we had to point out the numbers 1-20, in order, on a mixed-up grid. At the surface, I completed this in 30 seconds – at 105 feet, the same test took 50 seconds.  It is truly an interesting phenomenon.

Next, we had to use a compass to navigate around an imaginary triangle. Having always been a straight A-student, failing this exam three times was a pretty big blow to the ego. My partner succeeded effortlessly on his first try, which only added salt to the wound. Regrettably for him, we were a team – and he had to wait until I also passed the test before exploring the dive site.

Geometry not being my strong suit, I was pretty intimidated by the mere concept of a triangle – let alone how to navigate one by degrees. Attempt number one was a complete failure. Dive master Will stopped me midway, with a look of frustration, and had me try again.

Unfortunately, he didn’t show me what I did wrong, and I repeated the same mistake twice over. Worse, we had just missed an opportunity to swim with an enormous school of spotted eagle rays – I had seen at least 30 of them pass by in the distance. Before that moment, I had not known that it was possible to despise a shape.

By the time I finally passed the test and we caught up with the other recreational divers, dive master Pierre had found and captured a small orange squid. He passed it over to me so that I could feel the creature’s strong tentacles.

The suckers felt different than I had anticipated; for some reason I had imagined them more like cheap plastic suction cups. It jumped out of my hand (and, stupidly, straight back into Pierre’s), squirting black ink along the way. As it escaped once more, it released ink two more times before attaching itself under the crevice of a rock; it was hard to believe that so much liquid could come from such a tiny creature.

Now that I was certified for deep dives, we were going to explore Playa del Coco’s algae-covered shipwreck. “Don’t expect the Titanic,” Will warned. Expecting the opposite of the Titanic, I was pleasantly surprised to find that the wreck was indeed quite large – and equipped with various holes and windows that were perfect hiding places for fish and other marine life.

Looking for a decent spot to take a photo of the entire ship, I nearly bumped heads with a large white tip reef shark resting on the sand. Unafraid of sharks, I sat perfectly still, but found that the longer I looked into its cold eyes, the more nervous I became. Two other white tips began circling their way around me, and I could see  four or five more family members in the distance. Swimming away suddenly seemed like a very good idea.

So as not to make any sudden movements, I slowly edged myself backward until I was far enough to flick my body upward without clouding the predators’ personal space. Our dive group continued exploring until an enormous southern stingray appeared in the distance. Like the shark, it was also settled in the sand on the ocean floor. Easily as wide as I am tall and with a tail that stretched about seven feet, it was spooked by our presence and disappeared in the blink of an eye.

As we ascended, I noticed that Mike, one of the other divers, was holding an unopened champagne bottle. I wondered why I didn’t find things like that underwater. As we boarded the boat, Pierre explained that he planted the bottle in celebration of Mike’s 100th dive. He had secretly buried it under a rock 30 minutes prior to our dive. The entire boat was impressed with this clever trick. Summer Salt Dive Center has some seriously talented staff.

For more information, see our Playa del Coco travel guide.