WILLIAMSTOWN, Mass. -- The wait is over.

Art lovers who have been pining over their favorite pieces in The Sterling and Francine Clark Art Institute’s permanent collection can finally reunite with these classics now that the renovated Museum Building and new Clark Center have opened to the public.

The expanded and reconceived 140-acre campus had been ensconced in a multiphase, $145 million project for almost 15 years -- the most significant transformation of the Institute since it opened in 1955.

To accommodate the final stages of the project, all of the Clark’s galleries closed in March. Some of the permanent collection had been on a world tour for more than two years; it has returned just in time for re-installation in the newly renovated original museum building.

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During a preview tour for media, it was readily apparent that a team of acclaimed architects found common ground in making all three elements come together in a variety of ways.

The dominant element of the expanded campus is, by design, the natural surroundings, enhanced by the new one-acre reflecting pool. The water feature serves a variety of purposes, including a partial water supply for the campus. There is also talk of using it for skating in the winter.

Standing on the patio outside the new visitor center, gazing out over the reflecting pool, it becomes obvious that one of the designers’ goals has been realized: The pastoral setting is a beautiful prelude to one’s meander through the new and original galleries.

"The project advances the Clark’s dual mission as both an art museum and a center for research and higher education," said Michael Conforti, director of the Clark. "Since developing our master plan nearly 15 years ago, we have worked diligently to connect our program and support spaces with our extraordinary landscape, all with the goal of best-serving the thousands of people who come from all over the world to visit the Clark each year. What now looks simple and so logical, has been achieved through a complex and environmentally sensitive design and construction program that unites many disparate parts."

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Now, with more than 13,000 square feet of gallery space and improved climate controls, the Clark has much more flexibility in presenting exhibitions of both its own collection and visiting shows.

The new 42,600-square-foot Clark Center, which also serves as the main entryway to the campus and visitor center, was designed by Pritzker Prize-winning architect Tadao Ando. It includes more than 11,000 square feet of gallery space for special exhibitions and a multipurpose space that can serve as gallery space or for conferences and events. There are also new dining, retail and family spaces.

The original Museum Building expansion and renovation was designed by Selldorf Architects with more than 2,200 square feet of gallery space and the meticulously restored existing galleries.

The Clark’s campus was redesigned by Reed Hilderbrand and not only allows stunning views of a lush landscape, but incorporates a variety of sustainability initiatives. The three-tiered reflecting pool is also part of a cutting-edge water management system that reduces potable water consumption by roughly 50 percent, or 1 million gallons annually.

The project included expansion of walking trails, green roof systems, and the planting of 350 new trees. Even the new driveway and parking areas have water-permeable surfaces that feed into the rainwater collection system which provides the Clark with its nonpotable water needs.

"Reed Hilderbrand’s work has brought renewed ecological health to the land, helping to improve our significant natural assets," Conforti said.

The expansion project created more than 2 miles of public walking trails.

Throughout the project, although some trees deemed unhealthy were removed, about 1,000 new trees were planted.

Ando was on hand during last week’s press preview to talk about his vision and the reality that resulted.

"We spent 14 years on this project," the Japanese architect said through an interpreter. "Along the way there were moments we wondered if the project might be suspended or stopped altogether."

One person wondered how Ando’s design enhances the experience of the art lover.

Ando turned and indicated the glass wall facing out on the rich scenery of the Berkshires.

"By having this wall acting as an interface with the scenery, your perception becomes keener," he said.