Visitors can now press their faces to the reflective glass of the still-under-construction National Sept. 11 Museum, hoping to catch a glimpse of what lies inside.

The horror to the city, the nation, the nearly 3,000 people who died and to their family and friends, while 12 years ago, still bubbles up from time to time — especially on days like today.

At the building’s northwest corner are the two 70-foot tall “tridents” that stand as the remains of the north tower of the World Trade Center. They are defiant giant fists thrusting upwards and cursing that awful day. They need a middle finger, and from the interior museum steps, visitors will see through the windows that the new, nearly completed One World Trade Center fits that bill.

When it opens next spring, visitors will “follow the same path that hundreds followed as they escaped,” said Museum President and CEO Joseph Daniels. They will be brought through the first moments of that no good, terrible day to the later recovery efforts through the use of voices, personal remembrances and mementos that were chosen to commemorate and personalize the victims and praise the efforts and valor of the recovery workers and ordinary citizens who stepped in to help in the aftermath.

Each object was fully discussed through a “deliberate process” and “agonized over,” said museum director Alice Greenwald, who was previously with the Holocaust Museum in Washington, D.C.

The Survivor StaircaseLois Weiss

Although the above- ground building is a light and bright space, only family members will have access to a private room with views of the Memorial Pools and another private place at the bottom — Ground Zero.

Everyone else will troop underground, past walls of photos, voices and noises, past the lower walls of the Memorial Pools, and down either a long staircase or the escalator that flank the “survivor’s staircase,” which those fleeing on 9/11 used to get safely to Vesey St. and was left in place until the new World Trade Center building construction forced its removal.

A long hallway next to the Pool wall heads to a giant impact sculpture from the moment American Flight 11 crashed into the North Tower. Another turn, and a ramp takes visitors further underground, past more huge steel monsters that were twisted as the plane buried its nose in the tower.

The below-ground walls of the Memorial Pool have been covered in a nearly white aluminum pressed into ghostly lumps, a reminder of those who perished, as well as the Twin Towers that were also clad in aluminum. Over 1,000 victims left no shred of their DNA behind, Daniels said, adding that the city’s Medical Examiner will have a new office inside.

An overlook shows the cavernous room where the exposed slurry wall keeps out the Hudson River water. Here the “last beam” to be removed stands as a colossal, 75-ton reminder to the recovery workers who decorated it with the photos and the words of those they lost, including the FDNY’s Father Mychal Judge. The column is still wrapped in protective plastic.

Most of the exhibits and photos are not yet on the walls, and others are wrapped or swaddled in plywood to protect them from the construction dust.

Visitors will see the original bracing for the towers lying on the ground, and walk over portions of completely exposed and dusty Ground Zero.

Greenwald is hoping the expected millions of people a year don’t each decide to take a pebble or a scoop of it home, as happens with a petrified forest. They have also promised families, who consider this sacred ground, not to sell such “pieces.”

A another sensitive object known as a “composite” — a compressed meteorite-like mass of several floors that The Post first told you about in 2006 — is still hidden from view. That item as well as small photos of the “perpetrators” and the events leading up to their attack, will only be displayed in tucked away corners and so can be avoided by those disturbed by the images.

When it opens in the spring, there will be a charge of $20 to $25 per ticket, but Daniels insisted there will be free admission at least three hours a week as well as discounts. “We need to generate revenue,” he said.

In the Recovery area will be one of the lighter moments, as the sign “That’s All Folks,” from the Warner Bros. store will be displayed. Officials did not want that at the exit.

Other quotations are being forged from Ground Zero steel and will hang on the walls. These include one from Virgil that reads: “No day shall erase you from the memory of time.” Another from recovery worker and operating engineer Joe Bradley states: “We came in as individuals. And we’ll walk out together.”

Outside, visitors from many countries can pay tribute with flowers and other tokens they can place by the names of their lost loved ones. Tucked underneath the large name borders is a hidden place where children can safely touch the water. Almost no one notices.

It has become a place of reflection, as was intended.