Cellphone reception can be spotty at Glenstone, the Potomac, Md., art museum that is opening a redesigned campus, including a new 204,000-square-foot gallery space called the Pavilions, on Oct. 4. Signal is scarce in the large open-air courtyard of the cast-concrete building, where the only sound is water flowing through a lily pond, and the only glimpse of the outside world is a hawk circling overhead. Grasses planted on the green roof wave in the wind, and frankly, any thought of pulling out the cellphone vanishes.

Glenstone opened in 2006 as a quasi-public museum on the grounds of the estate of Mitchell and Emily Rales, accessible a few days a week by reservation only. The original iteration included a much smaller gallery building, designed by Gwathmey Siegel & Associates, which has since hosted critically acclaimed and focused exhibitions of artists collected by the Raleses. That space has become a pendant to the $200 million Pavilions building, a collection of 11 interconnected galleries set into a gentle hill, with the water court as the visual and aesthetic heart of the experience.

Visitors to Glenstone enter through a new gate on Glen Road, park in gravel lots with sycamore and oak trees for shade, and proceed directly to a minimalist reception pavilion. From there, a 10-minute walk through a spare, prairielike landscape, created by PWP Landscape Architecture, leads to the new building, designed by Thomas Phifer and Partners. Phifer’s vision is compelling: a building that is monumental but retiring, quietly grand yet never overwhelming, with a natural, easy flow around the water court, punctuated by galleries that occasionally frame views of the landscape. The grounds also include outdoor sculpture, paths and bridges, and a cafe that looks onto a thick patch of forest.

Everything is quietly spectacular, with curated views to the outdoors that present nature as visual haiku, while the interior feels uncannily like an architectural rendering, a ghost-scape of geometry and light and subtle shades of white and gray. But the spectacle has been sharply contained, framed and domesticated. Despite the rigor and finesse of the building, it feels utterly natural, except for the odd fact that it keeps presenting the visitor with strange visions: an outdoor room in which the floor drops out and a jumble of enormous metal beams (a sculpture by Michael Heizer) looks like some giant has played a reckless game of pick-up sticks; a large gallery with room for dozens of people that contains only one painting, by Brice Marden; a long corridor that terminates in a single sculpture, by Martin Puryear, which leaves you slightly in doubt of how big and how far away it is, until you make a closer approach.

The Raleses have used the freedom afforded by their extraordinary wealth to design what they hope is the ideal museum, a space perfect for the art they care about, free of the pressures that force other institutions to cut corners, compromise or follow the fads common to more-populist institutions chasing a wider, broader and more fickle audience. They have cited the inspiration of the Ryoan-ji temple in Kyoto, Japan, famous for its stone garden, which presents an idealized, distilled and symbolic view of nature, using only a few rocks and a backdrop of foliage seen beyond a low wall. The influence is obvious, especially in a room dubbed the “Viewing Gallery,” which features a long wooden bench facing a horizontal window that looks onto the rolling landscape with a thin fringe of trees arrayed like a screen in the distance.

Nine of the 11 rooms feature only one artist, while the largest gallery is devoted to an overview of the Raleses’ collection, featuring 65 works by 52 artists, made between 1943 and 1989. The original museum building also remains open and is filled with an exhibition that looks in depth at the work of Louise Bourgeois. So visitors have at least three modes in which to explore art: synoptically in the overview gallery, in depth in the old gallery and as a set of splendid, isolated vignettes in the rooms devoted to individual artists.

Tensions naturally arise — between the contemplative and the analytical mind, and between art and nature. There are rooms such as the overview gallery that are about thinking, history, the dynamics of influence and style, psychology and the social dynamics of art. And there are rooms that succeed or fail based on one’s susceptibility to more-irrational things, like the magic of a single work. And the natural world offers heavy competition when circulating through these contemplative spaces. Glenstone makes you keenly aware of the difference between the museum as a provocation to thinking and the museum as a place of purposeful thoughtlessness.

On a gray day this month, I found myself doing both. The art in the 9,000-square-foot survey gallery was a mix of important, canonical works by familiar names (Franz Kline, Jackson Pollock, Clyfford Still, Willem de Kooning) and brief chapters devoted to alternative histories, including a room of Japanese abstractions made in the 1950s and ’60s, and the Brazilian artists Lygia Clark and Mira Schendel. One large room within this subdivided gallery has been devoted to artists whose games with material and gravity set up a fascinating study in gender, and gender expectations, with a Richard Serra piece defying gravity with risky bravado in one corner, while a Lynda Benglis does the same with sleight of hand and whimsy on the far wall. This is a thinking gallery.

Nearby is a single room devoted to On Kawara’s “Moon Landing,” three of his black-and-white date paintings that reference days significant to the Apollo 11 mission to the moon. It is a tall, square room, with just one thing to think about, and if you’ve already thought about Kawara’s work before, it may feel like a shrine. That is an inherent danger with presenting work with a strongly conceptual edge in what many would consider ideal circumstances, a reflective space where nothing can distract from it. In isolation, the work feels like a problem to be solved, and once solved, what’s next? And with Kawara’s work, if you’ve thought it through before, seeing it again may serve more as a memorial to your earlier encounters than a fresh new goad to analysis.

The new Glenstone is the most significant addition to the Washington museum ecology since the opening of the Smithsonian’s National Museum of African American History and Culture two years ago. Most people probably will find that a half-day at Glenstone feels like only a first installment of taking its measure. And it will be interesting to see how it is received, what audiences make of its tone and peculiarities. There is no wall text to explain anything, although eager young gallery attendants will approach you to initiate conversations. Huge amounts of floor space have been invested in single works, such as Robert Gober’s elaborate installation of sinks and faux-forests and politically charged stacks of newspapers, a work that divides viewers along the usual fault lines of contemporary art, taxing the patience of those who find it hermetic, ensorcelling those who find in it a haunting dreamscape of death, escape and renewal. I found it tedious when it was on view at MoMA four years ago and overwhelmingly powerful when I saw it recently at Glenstone.

So on a single visit to this meticulously crafted new museum, I found myself thinking less of an artist whom I almost always admire and more of one whom I often find frustrating. I also spent a lot of time looking out the windows and thinking one, big heretical thought: Can any of this compete with simply staring at the grass grow? This is no slight to the stated ambitions of the museum’s creators, which was to create a place that would integrate art, architecture and landscape. They have succeeded in that, perhaps so well that the new Glenstone will put art to the test, unsettling judgments of its worth and meaningfulness, in ways both positive and discomfiting. It is a place that asks some of the oldest yet most relevant questions a museum can ask: What of all this matters? And what does it want from us?

Glenstone’s expansion will open to the public Oct. 4. Admission is free, but reservations are strongly encouraged. For more information visit glenstone.org. Museum hours are 10 a.m. to 5 p.m. Thursday through Sunday.