The ocean covers 71 percent of the Earth's surface and comprises 95 percent of the planet's livable space. It is, on average, as deep as 22 Washington Monuments stacked end to end. Only 10 people have explored it beyond 3 miles down.

Those are just a few of the facts you'll encounter when you visit the National Museum of Natural History's newly opened Sant Ocean Hall. True to its subject, it's the museum's largest single exhibit, with 23,000 square feet and hundreds of specimens and models on display. Sound a bit daunting? It is.

Here's a guide to a place that aims to both educate and astonish. Like the ocean itself -- which scientists have divided into the sunlit zone, the twilight zone and the deep ocean -- we've broken up its attractions into three groups.

The first, which we're calling snorkelers, is for surface swimmers. The second, for those who want to stay in a bit longer before they come up for air, is scuba divers. The third, deep-sea divers, is reserved for those who have no time constraints and want to sink as deep into the subject as they can.

Regardless of your diver rating, come on in. The water's fine.

The snorkeler

Phoenix the Whale: The Ocean Hall's theme could be characterized as "what lies beneath." But never mind that. As soon as you step into the place, you're going to want to look straight up. That's where you'll be greeted by the hall's unofficial mascot, Phoenix. Hanging from the ceiling, she's a 45-foot replica of a North Atlantic right whale. But not just any old North Atlantic right whale. This one is a kind of portrait, a scale-model model of a living whale that has been tracked by scientists since her birth in 1987. See those rough-looking bumps on her face? They're not barnacles, but callosities (similar to the calluses we get on our hands and feet). And their distinctive pattern is what helps trackers identify Phoenix from the air. You can even touch one of those warty growths at one of the Ocean Hall's several hands-on displays.

Giant squids: Next, head for that coffinlike metal case under Phoenix's tail. Inside? A 24-foot-long female giant squid, one of two specimens -- his 'n' hers -- preserved in a special hair-gel-like fluid developed by 3M. In a separate tank nearby you'll find a smaller, but no less eye-popping male. Now would be the time to take out your camera. The photo op -- you next to what appears to be the world's largest calamari appetizer -- is too good to pass up.

Giant great white shark jaw: The Ocean Hall's one must-see fossil belongs to Carcharodon megalodon, a now-extinct giant shark whose massive size (up to 52 feet) makes that other great white from the movies look like a goldfish. The teeth here are real. Only the jawbone itself, six feet tall when poised to chomp, is a reconstruction.

Coral reef: Clown fish and living corals abound in this 1,500-gallon aquarium, designed to replicate a coral reef ecosystem. Check out exotic species such as the exquisite wrasse, known for its ability to change sex in midlife. This is the Ocean Hall's only live display.

Coelacanth: "What is that thing?" a visitor was heard to mutter at a recent preview. OK, so the coelacanth (pronounced "SEE-la-kanth") will never win any piscine beauty contest, but it has an amazing backstory. Thought to have gone extinct 65 million years ago, it was discovered alive and well in 1938, when a South African fisherman caught one. The National Museum of Natural History is the only place in the world to have not one but two preserved specimens on display: a mother and her equally pug-ugly pup.

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