Though skyscrapers tower over the lush trees and sirens wail only a few hundred yards away, the Hallett Nature Sanctuary in Central Park is about as close as Manhattan residents and visitors can get to escaping city life without leaving.

The 4-acre fenced preserve, located just south of Wollman Rink and open to the public this summer on a newly expanded schedule, was one of the park’s best-kept secrets, open only sporadically since 2013.

However, its popularity has increased since it reopened April 1. More than 6,600 people, park officials said, have crossed through its rustic gate.

“Visitors have been amazed that such a beautiful, tranquil landscape exists just a few feet away from the hustle and bustle of midtown Manhattan," said Douglas Blonsky, president and CEO of the Central Park Conservancy, the nonprofit that manages the park.

Barry Donaldson and Bill Tripician of the Upper West Side were among those visiting Sunday for the first time.

"We've lived in the city for 45 years and walked around the perimeter (of the Hallett), but never went in,'' Donaldson said. “Through the years, I’d walk five to six miles through the park every day, trying to identify different types of plants. This is just fantastic.”

Along the trail are signs that identify ferns and sumacs, among hundreds of other species that form a habitat for birds and beneficial insects.

The sanctuary, previously called the Promontory, is a hilly peninsula jutting into the Central Park Pond. In 1934, too wild for human visitors, it was closed off and preserved as a bird sanctuary.

Fifteen years ago, the conservancy began revitalizing the wooded area, which had become overgrown with knotweed.

“Much of the work to restore the Hallett was performed by high school students,” said the conservancy’s Carla Sylvester. In 2003, the organization created a youth community service program, Restoration of the Outdoors Organized by Teen Students (ROOTS).

“Originally, the students’ work focused on eradicating invasive plants and building and maintaining trails,” Sylvester said.

The massive undertaking paid off for the health of the ecosystem.

“We began offering open hours in an effort to teach visitors what it takes to revitalize and care for a seemingly natural landscape,” Sylvester said.

This year ROOTS improved the paths by laying wood chips. Visitors can walk the trail in as little as 15 minutes or stroll along slowly and take everything in at their own pace. Guides are on hand.

At the top of the trail is an overlook of the reed-lined Pond and its waterfowl. Other Instagram-worthy photo ops include the base of a tree felled by Hurricane Sandy and the top of the waterfall that flows into the Pond.

To preserve the peacefulness, only 20 visitors are allowed in at a time.

“The only thing I didn't like was waiting in line to see nature — so New York,” said Deirdre Read, a Windsor Terrace resident and birder who visited in the spring.

Admission is free during open hours, which are from 11 a.m. to 1 p.m. Sundays, 2 to 5 p.m. Mondays and Fridays, and 2 to 7 p.m. Wednesdays through Aug. 31. Seventy-five-minute guided tours are available and have been selling out; admission is $10 for members and $15 for nonmembers.