Ask scuba divers what attracts them to the sport, and they’ll probably tell you that it’s the exotic underwater world. A dive in Japan, however, often means endless train rides, big crowds, small spaces and exorbitant sums of money — all too similar to the everyday world.

With an estimated half-million active divers here, it’s not surprising that the country’s best underwater sites are overrun. What’s a diver to do?

Fortunately, some of the world’s best diving is only a few short hours away, in Southeast Asia. With a discount flight and a carefully chosen package, you can enjoy tropical diving for no more than it costs to battle the underwater crowds at home.

The Philippines, a dive destination that draws people from halfway around the world, is only four hours from Tokyo. Many of the country’s 7,000 islands are surrounded by dazzling coral reefs, with spectacular new dive sites discovered every year. The downside is that travel to the most rewarding dive centers is slow and difficult — with one notable exception.

Puerto Galera, on the island of Mindoro, can be reached from Manila by bus and boat in three hours, a short hop by local standards. If you’re in a hurry to relax, a direct transfer by seaplane from Manila airport takes under an hour. Any way you arrive, the sight is stunning: A string of white beaches spreads against a mountainous backdrop. The deep, palm-lined coves once sheltered Spanish galleons bearing treasure from Mexico.

The beaches surrounding Puerto Galera town all have distinctive personalities, from serene White Beach to the raucous nightlife of Sabang. Many dive facilities at the major beaches have their own hotel and restaurant attached, with dive boats moored out front. You can make your first dive in the morning 15 minutes after rolling out of bed — or be sipping something cold in the bar 15 minutes after surfacing.

If you’ve always wanted to learn to dive, Puerto Galera is one of the best places in Asia to do it. Costs are reasonable (around $300 for a certification course), the instructors are seasoned pros and safety standards are high. The PADI Open Water course, which certifies graduates to dive anywhere in the world, is offered in English, Japanese and various other languages. The course can be completed in four days, and brings students face to face with barracuda and butterfly fish on their training dives, instead of just lost hairpins at the bottom of the local swimming pool.

The diving is tremendously varied, from a gentle paddle around a sunken fishing boat to the rip-roaring ride through the Washing Machine at nearby Verde Island. Many of the best locations are only 10 minutes away by boat, leaving more of the day free for relaxing. My husband and I came to Puerto Galera planning to stay five days, and instead stayed two weeks.

Our two best dives there were a study in contrasts. The site called Fish Bowl is deep and gloomy, with a fierce current bringing food that attracts some very big fish indeed. A white-tipped reef shark drifted over the sand, huge spotted sweetlips stared with big baleful eyes, six-barred angelfish did a ballet at the bottom and a solitary emperor angelfish swam majestic circles around a coral head. Battling the current, we hauled ourselves along hand-over-hand for half an hour. I surfaced sure that the rough dead coral had scoured my fingerprints right out of my skin, and wondering how fish manage to hover without moving a fin.

Our other favorite, placid La Laguna Point, is overlooked and underrated by many divers. We could actually see it from the balcony of our room. Yet the site was anything but dull. In a long, sunny dive, we encountered an entire underwater zoo: a half-buried flounder, shy darting razorfish, a lobster, baby lionfish and porcupinefish, a black ribbon eel — even a huge cuttlefish busily chugging along. The variety of corals is so great that our guide found a species that was new to him.

If even wading out to a dive boat is more effort than you like to expend while on vacation, you’re a candidate for a liveaboard cruise. As the name suggests, a liveaboard is a dive vessel with cruise accommodation. While many of them seem to be priced for millionaires, sailing yachts based in Phuket, Thailand, offer affordable trips to the Similan Islands, located 100 km to the northwest.

Cruising the Similans is pretty close to paradise: white sails, glorious beaches, and you emerge from your dives to succulent Thai curries served on deck. The islands themselves are nine uninhabited heaps of craggy granite covered in brilliant green jungle. The sand there is so pure and powdery that you sink up to your ankles. Behind the beach, monkeys screech and birds hoot, invisible in the dense foliage.

Underwater, the Similans are just as dramatic, and our seven-day trip visited two very different types of environment. The eastern face of the islands, toward the mainland, is lined with gentle sandy slopes and brilliant gardens of hard coral. On one memorable dive, at Swift Passage, we nearly landed on a sleeping leopard shark when we descended. He shook himself awake and ghosted off. We floated through clouds of tiny damselfish and glittering blue fusiliers, to find ourselves staring down at a bow-mouthed guitar shark, a peculiar creature that really does resemble its name.

The western reefs, facing out into the Andaman Sea, are deeper and wilder. Here, massive boulders form a backdrop for lacy billows of soft coral, and strong ocean currents sweep divers through a playground of archways and tunnels. At Elephant Head Rock, a dramatic formation of granite, dozens of barracuda cruised over our heads, silhouetted against the surface as we swam along canyons of red and purple corals.

There’s something magical about a liveaboard — sleeping rocked by the sea, drinking coffee on the deck at dawn, jumping into the water as the mood seizes you, slipping back in for a night dive as the last sunset colors are fading to black. Cruising the Similans is equally enjoyable for non-divers who want to go along and snorkel, or just laze on deck and enjoy the tropical scenery. It’s also possible to learn to dive during a cruise, as some crew members are qualified instructors.

On our last day in the Similans, at a site called Boulder City, a shadow passed over us as we were watching a shark. We looked up to find a 6-meter-long manta ray sailing above our heads. Having gotten our attention, he put on a spectacular display of rolls and dives, flips and somersaults. Finally, after 10 minutes of playful gymnastics, he made a long spiral and vanished out into the big blue.

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