Last week, a group of advocates filed an urgent Request for Evaluation with the Landmarks Preservation Commission for the Ambassador Grill & Lounge and Hotel Lobby at the United Nations Plaza Hotel (now ONE UN New York). These interiors, designed by Kevin Roche John Dinkeloo and Associates, and completed in 1975 and 1983, respectively, are spectacular luxurious rooms, which use mirror, pattern, and lighting to trick the eye into seeing palatial space, daylight, and high ceilings where there are actually none. The Roche Dinkeloo interiors are also among few intact examples of 1970s style left in the city, intended by the architects to draw the prismatic curtain walls of One and Two UN Plaza inside, creating a total work of architecture akin to that across the street at the United Nations proper.

The request was urgent because, though no permits have been issued by the Department of Buildings, Millennium Hotels has made no secret of their plans to update the property. The windows to the Ambassador Grill were recently papered over and Docomomo US reports that some exploratory demolition has taken place—illegally. I urge the Landmarks Preservation Commission to hold an expedited hearing and to keep close watch over 44th Street.

We should not allow a repeat of what happened to Frank Lloyd Wright's Park Avenue Mercedes Benz showroom: demolition when no one's watching. Those who were watching, this time, include Liz Waytkus, Executive Director of Docomomo US, with assistance from Daniel Paul, a Los Angeles-based architectural historian, architect Kyle Johnson, Guest Curator of the 2011-2012 "Kevin Roche: Architecture as Environment" exhibition, and landmarks advocate Theodore Grunewald. The campaign also has the support of the Historic Districts Council, which commended on Facebook: "It isn't often we defend shiny glass spaces—but this one is special."

One might ask, if the UN Plaza Hotel lobby and the Ambassador Grill do not rise to the level of an interior landmark, then what? What might meet the standard? The Landmarks Preservation Commission has historically been loath to landmark interiors, but here is one that is (as required) a public space, over the 30-year age limit for consideration, largely intact, by a still-living and Pritzker Prize-winning architect responsible for numerous New York City monuments, that is still wanted for its original purpose. It doesn't get any better than this, landmark-wise, but for (of course) the lack of interest of its owner in keeping it. It is hard for me to imagine a new design that would improve upon the old in making a box-like hotel lobby and an underground room with no windows into an amusing, intimate, and exciting destination. Go look at the lobby for yourself.

What Roche Dinkeloo was trying to do on 44th Street was a design task parallel to the one they had undertaken at the Ford Foundation on 42nd: to make the interior of the building speak the same language as the exterior. The architect's desire to create a total environment returns, but now at a far larger scale than the house. At the Ford Foundation that means a symphony in the key of brown: brown granite, Cor-Ten steel, mahogany, with brass and greenery and lots of glass to brighten it up. At One and Two UN Plaza, it meant orchestrating mirrors, wrapping the reflective prisms of the skyscrapers' exterior grids (potential landmarks themselves) inside and—not incidentally—making interior and underground spaces feel like a greenhouse. According to the late architecture critic Herbert Muschamp, Rem Koolhaas used to stay at the UN Plaza and the faceted exterior of OMA's Seattle Public Library shows the influence.

You can enter the restaurant from two points. One entrance is directly off 44th Street, under a chic neon sign suspended over a welcome mat of black-and-white triangular pavement. A long hallway lined in reflective black leads you back. Or you can enter under the hotel's glass awning, stepping from the street underneath Roche Dinkeloo's stepped, mirrored octagonal dome. More triangles, this time in white and dark green marble, suggest that you step to the center and look up. To one side is a long, ramped hallway, topped by mirrored coffers fitted with tiny, twinkling lights. Chamfered columns alongside the hallway are mirror and marble on alternate sides.

At the end of the hall, the most photographed piece of the puzzle: An octagonal stepped mirror that draws you down but is angled so you are still looking at refracted bits of the lobby, rather than at yourself. Period photos show a large and glorious flower arrangement in front. It is here that one can see Roche Dinkeloo's work transition from late Modernism to Postmodernism, reimagining a Venetian corridor in a 1970s Midtown hotel.

The restaurant uses more of the same materials: checked marble floors and red carpeting and banquettes are reflected in a dropped, reflective ceiling made of stretched mylar panels. As Ada Louise Huxtable wrote, “That ceiling, which appears complex, is simple design ingenuity. A kind of greenhouse roof is set into it, and above the glass are pentagonal mirrors and myriad small lights that make a fantasy of reflection and illumination. Against this visual intricacy, everything else is held in restraint.”

That restraint will serve contemporary restaurateurs well; reduced to black-and-white and mirror, the design of the Ambassador Grill does not speak to any particular country or cuisine. Tweak the chairs (the original pale bentwood seats are long gone), tweak the tablecloths, tweak the plants, and you could be somewhere else. The only artworks in the space are ethnic embroideries mounted in acrylic boxes—a choice often made by Girard—in this choice, Huxtable wrote, "The architects have even come to grips with that universal hotel horror, the pictures on the walls."

It is an ever-present irony of preservation that our culture often takes buildings down just at the moment they are ready for re-appreciation. So Bertrand Goldberg's Prentice Women's Hospital in Chicago disappears in 2013 and 2014 (demolition takes time), and his Marina City towers are landmarked in 2015. Paul Rudolph's Orange County Government Center is demolished in 2015, a year after the first critical biography on the architect and in the same season as the publication of Heroic, an examination of the urban legacy of concrete architecture. Though One and Two UN Plaza, built between 1975 and 1983, stand right on the dividing line between Late Modernism and postmodernism, it is safe to say that this is an opening salvo in the battle to save postmodernism in New York, as it ages in to our landmark process and begins its own re-appreciation process. In 2014, Metropolis published a handy guide to what to look out for.

One block from the UN Plaza towers, the landmark Ford Foundation, also designed by Roche Dinkeloo, with a landscaped atrium by Dan Kiley and interiors by Warren Platner, is undergoing what one hopes will be a respectful renovation. Ford Foundation president Darren Walker "disabused the renovation architects, Gensler, of any idea that they could remove the 5,000 pieces of furniture by Mr. Platner and Charles and Ray Eames. As much as possible will be reused," Walker told the New York Times. In March, the Vitra Design Museum will launch "Alexander Girard: A Designer's Universe," the first exhibition and catalog to draw upon the polymathic designer's archive. La Fonda del Sol, Girard's 1960 Mexican modernist restaurant in the Time & Life Building will be featured.

Girard and Platner were both longtime collaborators and colleagues of Roche Dinkeloo, and their interiors speak a common language. The Ambassador Grill is the only intact example of the glamorous dining establishments that followed in the footsteps of Philip Johnson's Four Seasons Restaurant (now undergoing its own contentious updates). Girard contributed La Fonda and L'Etoile (1965), a French restaurant in the Sherry-Netherland Hotel kitted out in black-and-white, with tables in the form of white flowers. Platner created first the Ground Floor restaurant in Eero Saarinen's CBS Building (1965)—an all-black interior with a gridded mahogany-and-brass ceiling ("like eating in a coal cellar," said one critic)—and later Windows on the World (1977), which, like the UN Plaza Hotel, greeted visitors with a crystalline, reflective lobby. The lobby and the grill stand on their own, but they also stand for two decades of lost glamor.

The more period commentary on these spaces you read (by Huxtable, Paul Goldberger, and Carter Wiseman), the more you see the hotel's owners are falling into the very trap the interiors were engineered to escape: banality, anywhere-ness, the flimsiness of changing fashion. Hotels then, as now, were not typically a space of theatrical experiment (John Portman excluded; keep an eye on his Marriott Marquis in Times Square). Are the current going to rip out the mirror and replace it with barn wood and mason jars? Just wait. Stop the unpermitted demolition. Landmark this interior and, in doing so, remind people of its undated and undateable wonder.

· Kevin Roche's UN Plaza Ambassador Grill and Lobby Closed, Pending Demolition [Docomomo]

· Remembering Frank Lloyd Wright's Bijou [Metropolis Mag]

· All Landmarks Preservation Commission posts [Curbed]

· Peek Inside 9 of New York City's Pristine Interior Landmarks [Curbed]