Ask Jeannette Auber, owner of boutique Kauai dive shop Fathom Five Divers, what scuba diving means to her, and you’ll have an idea about the experience that awaits you as a diver when you head out to explore some of the most spectacular underwater sights in all of Hawaii with the Fathom Five team. Kauai, which is the northernmost island in the Hawaiian archipelago, is nicknamed “the Garden Island.” A drone’s-eye view reveals why: This postcard-pretty island is draped in emerald rainforest and valleys and surrounded by the brilliantly blue water of the central Pacific Ocean. Like its topside scenery, Kauai’s dramatic and lush underwater topography has been forged by Hawaii’s volcanic history.

“I discovered diving in 1990 and it changed my life–so that it is my life,” Jeannette says. “Everything I do has just evolved from the passion I have for diving.”

Before she took the helm in 2001 at Fathom Five, Kauai’s longest-operating dive shop, Jeannette had plenty of experience learning what she ultimately wanted in her own boat and shore diving operation.

“I wanted small groups of divers so we could provide a personalized experience as well as to really try to educate people about marine life,” she says. Inspired by her vision, Fathom Five has evolved into not only the gateway to Kauai’s epic shore and boat diving but the island’s epicenter for dive education, too.

Today, the family-owned and operated shop–Loni Adams, Fathom Five’s general manager, is Jeannette’s son–gives curious divers a true taste of the diversity and wonders that await off Kauai’s verdant shores and on neighboring Ni’ihau Island (known as Hawaii’s “Forbidden Island”), too.

Loni’s relationship with the ocean began at a young age in Santa Cruz, California, where his father was a professional surfer. And it continued in Kauai, where he later relocated with his mother and ultimately ended up becoming a dive instructor in 2002 to run the shop with her. You’ll find mother or son in the water or in the shop on most days at Fathom Five. The shop’s two dive boats regularly visit 15 dive sites just offshore from Kauai, all of which can be reached in under 15 minutes from the harbor. So by the time you step onboard the dive boat, double-check your gear and zip up your wetsuit (all of which has been brought down to the boat from the shop for you), it’s nearly time to get into the water.

Spend your days doing two- or even three-tank boat dives to interesting reef and ledge formations frequented by Hawaiian green sea turtles and whitetip reef sharks at sites such as Sheraton Caverns and Turtle Bluff, among others.

“Almost 25 percent of the marine life in Hawaii is considered endemic,” explains Jeannette about the unique marine environment surrounding the islands. “We are the most isolated piece of land anywhere in the world—the closest major landmass is over 2,000 miles away.”

For experienced divers, there’s no better boat expedition than the one to Ni’ihau Island, an island full of lore for Hawaiians and one of the most mysterious islands in the chain. Though it takes about two-and-a-half hours to reach from the harbor in Kauai, there are huge rewards that you’ll start reaping as soon as you enter the water for the day’s three dives here.

“Diving Ni’ihau sort of incorporates all the best of all the Hawaiian islands,” Jeannette says. “We dive around a crater. There’s drifts, walls, arches, pinnacles. Ni’ihau has everything.”

The biggest thrill for most divers who venture to Ni’ihau is the chance to spot the rare and highly endangered monk seal, commonly seen by divers in these crystal-clear waters. And with no more than six divers at a time on any of Fathom Five’s boats, you can count on the experience being as intimate as it is unforgettable.

“Our dives are all about adventure, education and respect for the marine environment,” says Jeannette, something you’ll feel with Fathom Five on every trip.

Back on Kauai, divers are sometimes surprised to learn that the Hawaiian island that’s so famous for topside adventures–hiking, helicopter tours, ATVing and all manner of other adventure sports are standard fun here–also has some of Hawaii’s most epic shore diving.

And with a guide from Fathom Five to lead you through the local waters, you’re in for an incredible experience. Kauai’s shore diving season runs year round, except for Tunnels, which runs May through September. Sites such as Tunnels–off Makua Beach, on the island’s north shore–beckon with caverns you can weave in and out of as you explore the inner and outer reef. For both Jeannette and Loni, early dives at Tunnels form some of their core Kauai diving memories. They both credit the site with getting them hooked on the island’s shore diving.

“Kauai has more of a shelf around it than the other islands, and this is where you’ll see a lot of the endemic species,” says Jeannette, naming endemic lionfish, sergeant majors and conger eels among them. And if it’s turtles you long for, Kauai is the place. “Green turtles are the most abundant turtles around the island, and you might see the occasional hawksbill, too,” she says.

“Depending on the tides, we will drift dive when conditions are right, starting at one site and ending on another,” says Jeannette.

When you plan your dive vacation to Kauai to time with the humpback whale migration, the rewards run even deeper.

Humpback whales arrive in Kauai’s waters starting in September to calve their young, sticking around the island through March.

“The best months for hearing and seeing whales during dives are January through March,” says Jeannette. “Every year we see whales underwater, too, and you never know which dive and divers will be the lucky ones.”

Jeannette and Loni create dive itineraries based on the season, conditions and what their guest divers would like to experience. “We want our customers’ input on where they want to go, and then we’ll be the experts on whether it will be good that day based on currents and visibility,” she says.

It’s what makes diving so exciting in this remarkable place–even for people like Jeannette and Loni, who have been diving these same sites on Kauai for decades and counting.

“You just never know what you’re going to see underwater in Kauai,” she says.