The Philadelphia Museum of Art is tearing itself apart in plain view. Here’s what to know as construction ramps up.

Well over two years into the ongoing interior transformation of the Philadelphia Museum of Art, and more than a year out from the end of the massive undertaking, visitors are experiencing some challenges.

The roadway up to the west entrance can be a bit dicey at times, with construction vehicles, equipment, workers, broken paving, closed walks, cyclone fences, and street barriers forming a kind of obstacle course, summoning up the intrepid museum-goer’s most creative skills of navigation.

Once inside, many things aren’t necessarily where they were in the not-distant past. Wings of the museum and stairways are blocked off. Galleries are closed. Artworks have moved. (How do I get to the restaurant?)

Enormous, sealed, white barriers flank golden Diana in the Great Stair Hall, harbingers of yet more demolition to come. Beyond the wall behind her, elaborate scaffolding encases staircases and the wall at the rear of Lenfest Hall, the west lobby, foreshadowing the same demolition.

Clearly the museum is attempting an unusual feat: Tearing itself apart in plain view, but hiding the mess.

Given the magnitude of what museum officials call the “Core Project” — the latest, intense phase of a decades-long makeover masterminded by architect Frank Gehry — the miracle lies in the fact that the museum has managed to remain open throughout construction.

After all, the central heart of the building is being demolished and rebuilt, along with the interiors of two wings jutting north and south that have already undergone most of their interior demolition. (They’ll emerge in 2020 with 25,000 square feet of new gallery space.)

Yet, despite the intimidating construction, in 2017 attendance to the museum hit 793,000, “a good number for us,” said Timothy Rub, director and chief executive. “This past year, in the midst of the Core Project, it’s over 770,000 visitors,” he said.

“We’ve been doing these exhibitions around the collection, and people are continuing to come," he said. "Even though it is a pain in the ass to twist ourselves into a pretzel to stay open during all of this, we’ve maintained strong membership and we’ve maintained strong visitation. We’ve been able to keep our entire staff at work, no layoffs. That’s nice. It’s been a challenge, but it’s been the right thing to do.”

The Core Project is scheduled to end completely by September 2020, but parts of it are already done (renovation of the east wing’s ground floor and the opening of new food services), and some spectacular elements (the new vaulted walkway entrance) are due to be ready in about two months.

But the next phase of Core Project construction will bring the biggest problems for those wandering inside the great Neo-Classical building at the end of the Benjamin Franklin Parkway. For one thing, the west entrance — the entrance on the side away from the Parkway — will close in September.

Already, two great sculptures that had flanked that entrance for decades have been removed and relocated to the University of Pennsylvania campus. The west terrace will soon be torn up and redone with new paving, stairs, and ramps, reopening in September 2020.

The good news is that with the west entrance closed, access to the museum (from the parking garage, for instance) will be through the spectacular vaulted walkway, a tile-sheathed tunnel-like space that runs 640 feet from the museum’s Kelly Drive side to its river side. The walkway, currently being renovated, was closed to the public in the 1960s and served as a loading dock until 2012, when a new “art-handling facility” opened on the museum’s river side.

Half of the walkway will reopen to the public in September (including a coffee bar and a gift shop, of course). The rest will open in September 2020.

With the closing of the west entrance and opening of the vaulted walkway, Lenfest Hall, the west entry salon, will undergo a major renovation and refurbishment.

The old auditorium, once located in the heart of the museum, just beyond the rear of Lenfest Hall, was recently demolished. But now the rear wall at the end of Lenfest Hall all will come down, opening up the interior of the whole building and making way for construction of what the museum calls the “Forum.”

The Forum is a fancy name for what will function in part as a visitor distribution center, drawing people in from the Lenfest Hall and the vaulted walkway and wafting them up through the rest of the museum and to newly opened galleries of American and contemporary art. The east entrance, up the Rocky steps, will remain open throughout.

If this seems like a dizzying set of changes, it is. But the ultimate effect will be logical, as a recent walk through the construction site made clear.

From the vaulted walkway, which runs directly beneath the east facade of the museum, much of the major demolition is easily visible.

Walls of subterranean parts of the museum are being removed, spilling mountains of red bricks everywhere, and huge beams are being inserted to support the museum’s eastern facade and columned porch.

The demolition and construction has had its uncomfortable moments. For one thing, contractors engaged in digging to lay all new utilities — a critical part of the entire effort — encountered much more bedrock than anticipated. They also encountered lots of asbestos, requiring expensive abatement.

As a result, in part because of such unanticipated events, the budget for the Core Project has climbed from $196 million to $228 million. But it now also encompasses renovation of one museum wing and the opening of the new museum café and its restaurant, Stir. That renovation was a late add-on to and was not included in the initial $196 million budget.

While Rub said he was not ready to provide numbers at this point, fundraising is “on schedule” and “proceeding according to plan.” Announcements with specifics will be forthcoming by fall, if not sooner, he said.

Demolition and renovation of two wings stretching north and south from the museum center is also proceeding.

On the north side, where old executive offices were once housed, demolition is complete and gallery spaces are demarcated.

Here is where contemporary art will occupy 12,500 square feet of new gallery space.

The windows have been replaced and the Tiffany ironwork has been restored. The corridor has been moved, enlarging the future gallery areas and allowing light in, opening the building exterior to the city beyond.

Gail Harrity, museum president and chief operating officer, cast her eye over an expanse of cement floor pocked by islands of empty buckets of spackle, wires hanging from metal trusses in the ceiling, stacks of metal wall braces, and said, “This was Anne’s old office,” referring to the late museum director and chief executive Anne d’Harnoncourt, who died in 2008 and who launched the museum transformation.

“Essentially what we’ve been doing is emptying the main building over the last decade or more to [devote] this building for the public, for collections, galleries, public amenities, and education programs,” Harrity said.

On the other side of the building, in the south wing, where the museum restaurant and gift shop once were located, another 12,500 square feet of new gallery space is being readied for American art up to 1840.

That space, said Kathleen Foster, the museum’s senior curator of American art, will allow for exhibition of artworks with an “inclusiveness that will be a surprise” to visitors. The art of Native Americans, Latin Americans, and African Americans will be enfolded into the museum’s narrative, she said.

“We’ll bring those stories to the forefront, which we’ve never been able to do before,” Foster said.

If this wasn’t enough, the museum has also begun a refurbishment of its 19th-century European art galleries off the Great Stair Hall — quite apart from the Core Project, but done in concert.

“It’s the first opportunity in 25 years to rethink how we present the second half of the 19th century,” said Jennifer Thompson, head of the museum’s department of European painting. She said galleries will be presented thematically.

The reinstallation should be complete by early 2020, she said. But for now, impressionist works occupy the museum’s summer impressionist exhibition and three 19th-century galleries are closed.

And despite all the topsy-turvy, the museum has managed to keep all its signature works in place.