When your instructor hands over a fresh C-card, it might be the end of your scuba diving course, but it’s only the beginning for so much more. Once you’re a fully certified Open Water Diver, thousands of possibilities arise. And no one gets certified so they can just practice skills in a swimming pool.

Now is the time to get out a pen and paper, pull up a map of the world and start making your scuba diving bucket list to help fill out your logbook with the most amazing experiences the underwater world has to offer. Divers are free to explore historic shipwrecks, get up close and personal with apex predators, find Nemo, venture into caverns and browse underwater museums.

There’s something for everyone out there.

Here are 15 mind-blowing experiences to get you started.

Encountering a giant manta ray is one of the most humbling and intimate experiences a diver can have. A manta will meet your gaze, seeming to ask questions. Moreover, a manta can hover, so the two of you can hold that eye conversation for as long as you like, or as long as the tank lasts, whichever comes first. For encounters, Hawaii Island (aka Big Island) delivers some of the world’s best odds thanks to weekly night dives with the filter-feeding animal. Granted, at night, mantas are feeding on the plankton that’s drawn to the lights, and so for a more leisurely, personal encounter, ask to visit these same spots by day.

Ah, the clownfish. Ever since Nemo — an Amphiprion ocellaris, or common clownfish — stole our hearts, this fish has topped underwater must-see lists. Only divers can witness up close their shy behavior, and study each long enough to identify it among 30 species. Of course, the Coral Triangle is a choice destination for encountering many on the species list, with the Raja Ampat Islands delivering five or so at nearly every site. And with a clownfish sighting comes the chance to appreciate the beauty of the anemone, a flowerlike cnidarian that holds a symbiotic bond with the clownfish.

Divers know the tricks: Start a seahorse search by visually combing the rope sponges. Scan for that distinct profile that’s all angles. And that twiglike snout, instantly recognizable. That hunt, as thrilling as victory, can last as long as your tank does. When the search proves successful, then it’s time to enjoy watching the flutter of that gossamer-wing dorsal fin, slowly moving it forward. The tail, much like that of a monkey, is prehensile — that is, capable of grasping — and grips onto blades of eelgrass and the like to stay put in its fluid home. On Bonaire, look under docks and piers when making house-reef dives.

Only ­divers can spend time on the sheer backside of this crescent-shaped volcanic formation found an hour by boat off the coast of Maui. Snorkelers stay within the protection of the crater, swimming with schools of butterflyfish. But divers venture to the unprotected outside, where faster-­moving water makes for gnarly drift dives alongside the predatory bigger fish, from amberjack to whitetip sharks. Giant manta rays and blacktip sharks are also possible sightings in this 160-foot-deep arena.

Credit this island nation’s exploding population of anthias for creating reefs that are a riot of color. These fish drift like pink, red and orange clouds overtop forests of soft corals, blooming in similarly fiery hues. Add in the anemones, housing clownfish and shrimps. Then consider the eels, the nudibranchs and the cuttlefish. Admit it: It’s pretty, and you like it. Sure, you can tell friends that you really traveled to Fiji for the sharks, schooling jacks and the whole lot of deepwater excitement. But we know the real reason, and your secret is safe.

Captivating as it is to swim in the impossibly clear water of a cenote, it’s even more mesmerizing to venture beyond the entrance. To where stalactites hang, sometimes packed together like matches in a box, as in the cenote Dream Gate. To where pockets of hydrogen sulfide gas create layers, gauzy and dreamy as clouds, as in Hells Bells Cenote. From crepuscular rays of sunlight streaming in from overhead openings to gnarled trees sprouting from the depths, each packs its own wild ­combination of wonders.

A snorkel encounter with the world’s largest fish sends one’s heart racing — but can be limiting in terms of viewing position. In places such as the Maldives, which happens to have a year-round population of this spotted giant, scuba diving is permitted with the animal. So long as divers don’t affect the animal’s direction of travel, they’re allowed to swim under, alongside or in front of the shark. A bonus: Bubbles tend to spook most marine life, but this fish often mistakes bubbles for plankton, and fins in closer.

Dive a marine cave, and along with stalactites and the typical formations, you’ll also find reef fish. In Palau, the most famous such site is Chandelier Cave, with mandarinfish flitting about near the entrance. What’s more spectacular is that the four chambers have air pockets, so divers traverse the dark tunnels, then pop their heads from the water to see a ceiling supported with ­formations big as columns.

Before they were named an endangered species in 1976, Hawaiian monk seals could commonly be seen napping on sunny beaches of the 50th state. But increasing coastal development limited their habitat, leading them to favor the uninhabited northwestern Hawaiian islands — and, more convenient for divers, the island of Ni’ihau, 18 miles west of Kauai. Here, this silvery seal, one of the world’s few species to live year-round in more-tropical waters, can be sighted off Lehua Rock. On two out of three dives, a solitary male can be seen guarding territory, fixing his large black eyes on anyone who nears.

From the surface, Darwin’s Arch appears as little more than a wonder of nature-carved rock. Up there, the biggest action is crashing waves and bird sightings. Drop in below and take a seat at the dive site known as the Theater to watch all the reasons divers drool over the Galapagos: It’s only a matter of time before whale sharks, schooling hammerheads, silky sharks, bottle­nose dolphins and every other hungry marine animal take the stage.

The bunnies of the sea, green sea turtles possess that big-eyed look of innocence, and seem most content when grazing on algae. Divers love them because they toe that line between acting curious and timid, allowing for long encounters, so long as quick, darting movements are avoided. A good place for a meet-and-greet is off Grand Cayman’s western beaches, from Georgetown on the southern end up to — no surprise here — Turtle Reef to the north.

The life-size figures crafted by sculptor Jason deCaires Taylor act merely as a foundation. Since the inception of the first underwater sculpture park in Cancun, Mexico, installed in 2009, each work has become a habitat for sea fans, budding coral, sponges, and shrimp and other crustaceans, nibbled at by parrotfish, grunts and snapper. The artist himself recommends viewing the works at night, limiting your view to only what your light can illuminate.

Don’t forget to look up toward the surface when you’re deep within this 150,000-year-old sinkhole. This is the view that only divers can behold. The Great Blue Hole is found in Lighthouse Reef, one of Belize’s three major atolls. To be in the middle of this opening, 1,043 feet across, surrounded by stalactites as large as the divers there to bear witness, and gazing up at the sun streaming into this nearly perfect circular opening — from this vantage point, one can truly appreciate natural wonder.

Most divers prefer their wrecks intact and upright. Picture-perfect. Clear visibility, some 90 feet or greater, only adds to the experience. In the Bahamas, off the island of New Providence, the 200-foot Ray of Hope freighter offers precisely this, sitting on sand that slopes from a depth of 40 to 60 feet. Perhaps most enticing of all is that this purpose-sunk wreck is the cruising ground of dozens of Caribbean reef sharks, which dials up the adrenaline for ­divers exploring the upper deck.

There is no single ­animal encounter that makes the world’s largest coral-reef system — all 900 islands spread over 133,000 square miles — such an enviable experience. Rather, it’s the diversity of encounters, from scores of great humphead parrotfish swimming past to spying giant clams, 4 feet long and riddled with ribbons of iridescence. And of course, clownfish. Perhaps most magical of all is the June and July migration of curious minke whales.