Ambika the elephant stood in the sun, curled her trunk around a pile of golden sand and flung it onto her back.

This was fine river sand, and as it fell off her body, it caught the light and looked like a shimmering gown.

Against the backdrop of green bamboo waving in the breeze outside, it was a delightful scene. But for the 65-year-old Asian elephant with one “finger,” 18 toenails and a nervous disposition, the National Zoo’s new Elephant Community Center still held some fright.

The spacious, sunny indoor center is the final piece of the zoo’s seven-year, two-part, $56 million project to create a state-of-the-art Elephant Trails complex and increase the size of its herd.

The first phase, which included a 5,700-square-foot barn, two new yards, a pool and a quarter-mile walkway through woods, opened in 2010. The community center — which the elephants are still getting used to — opens to the public March 23.

To the animals, the center is still unfamiliar in its size and layout. Its interior is much bigger than the zoo’s old elephant house, and it’s now an elephants-only hangout. The old digs had to be shared with hippos, giraffes and hundred-pound South American rodents called capybaras.

One day this week, Ambika, a former rescue elephant from India, couldn’t bring herself to enter the scary emptiness of the new Stall 7. Plus, she hasn’t yet realized that if she steps on the pedal near the pool, it turns on the shower.

“This is still a place that they’re exploring,” said animal curator Tony Barthel. He said the elephants were introduced to the center about a month ago. Since then, keepers have been coaxing and urging the animals to use the center.

It’s crucial to get the elephants comfortable in the new space, for their safety and that of the keepers, before opening to the public, the zoo said.

Right now, three-ton Ambika — the third-oldest elephant in North America — shares elephant country with another female, Shanthi, who is about 38 and weighs four tons, and Shanthi’s son, Kandula, 11, who weighs about three tons. All are Asian elephants, which are critically endangered.

The new center has a four-foot-deep layer of sand, a cushioned floor in another enclosure, and lots more room.

For now, the complex is home to just the trio. But Barthel said the zoo is working to acquire more. “That’s a big goal of ours,” he said. “It’s a very long process [but] we’re ready now.”

The zoo’s veteran elephant manager Marie Galloway said: “One of our visions is that we will have a flourishing community of elephants.”

“We could house eight to 10 elephants here, easily,” she said. “We have two spots for males to be completely independent. But the entire facility is bull-proof.”

Indeed, the new enclosure, for all its sun-filled openness, is made with concrete doors, heavy steel girders and thick stainless-steel cable. Kandula, the adolescent male, could eventually grow to be a truck-size, six-ton behemoth, Galloway said.

There’s also an elephant restraint device, a kind of giant steel stall that can be used for medical procedures, and a ceiling hoist that Galloway said will be used only in critical health situations.

“Hopefully, you never, ever, ever need to use one,” she said. “But if you do need it, it can mean the difference between life and death.”

As she showed off the new center Tuesday, she talked about the animals’ personalities.

Ambika is “nervous about new things,” she said. “She doesn’t like change. She stresses more easily. . . . She needs to know that everything’s okay.”

And as Galloway spoke, Ambika doused herself in clouds of comforting sand.

“It protects their skin from sun — they can actually get sunburned — and from bug bites,” Galloway said. “And sometimes I think it’s just plain fun. I think they do it in the winter, too, as kind of insulation in the cold.”

The elephant grabbed a bamboo stalk that had been offered by a keeper. She stepped on the stalk with one foot and began to strip the leaves off with her trunk.

Elephants have five toes on each foot but only four toenails on each of the back feet. And Asian elephants have an appendage at the tip of their trunks, called a finger, that they use to grasp.

The trunk “can pick up something that’s thousands of pounds but also can pick up a single blade of grass,” Galloway said.

Ambika has been at the zoo since 1961. She had been captured in India when she was about 8 and put to work in a logging camp. After about five years, she was given to the zoo by the children of India, according to the zoo.

She survived a blood clot back in 2007. And though graceful, she tends to be timid and cautious.

Shanthi was a gift from the children of Sri Lanka in 1976. She is more bold and inquisitive. Kandula, her son, weighed 325 pounds when he was born in 2001 and is rambunctious.

The elephants talk to each other through a range of vocalizations that includes a very low sound called a rumble.

“They squeak and chirp and honk and rumble — and roar,” Barthel said. The roar is stunning, he said. “It sounds like a T. rex.”

But there’s little to grouse about. A daily bath. Regular pedicures. Food all day long.

And now plenty of room for new guests.