Architect Paul Udris has designed one-of-a-kind spaces all over the world, from Manhattan to Morocco, but none of them was quite like the commission he landed from longtime friend and past client Horst Rechelbacher, the founder of Aveda and Intelligent Nutrients.

In late 2011, Horst bought the entire unfinished top of floor of the Phoenix on the River, a luxury high-rise condominium building overlooking the Mississippi River and downtown Minneapolis, and hired Udris and his team at U+B architecture & design to transform two connected units into a single 12,000-square-foot penthouse, creating what was believed to be the largest condominium in the Upper Midwest.

Horst, who died early this year, wanted the space to be not only a home but also an art gallery for his vast and eclectic collection of turn-of-the-century Viennese treasures. And he wanted the complete transformation to happen quickly, in less than a year.

For Udris, the most formidable challenge was stitching together two units within the confines of existing plumbing and electrical systems, to create what he described as "a contemporary palace in the sky."

Q: What did you think when you first saw the space?

A: I've never done a project with a better view. I was awe-struck by the views, which include all of downtown from the north side, as well as the entire downtown Mississippi waterfront, including St. Anthony Falls.

The penthouse condo comes with a 270-degree view of the downtown Minneapolis skyline and the Mississippi River, plus multiple patios and terraces, offering an ideal vantage point during downtown fireworks displays, such as during the recent Aquatennial.

Q: What did you like best?

A: The views are, of course, without equal, but I was also excited by the two two-story spaces at the corners, which give additional drama to the space.

Q: What was the trickiest part of the project?

A: The space was originally conceived as two apartments, with many more closed rooms, so there was a great deal of infrastructure from the floors below that we had to work around and/or relocate in an effort to make the space as open as possible.

Q: Horst had several homes, including a New York penthouse that you designed for him and a Wisconsin farm — what was the primary design objective for this place?

A: To create a clean, bright, open space for showcasing a fabulous art collection and entertaining on a grand scale.

Q: Did you have a budget?

A: Every project we work on has a budget, and we needed to think carefully about how to maximize the efficiency of the construction process and the material selections to stay on schedule and within the budget.

Q: What's your favorite space, and why?

A: I love the main staircase, especially when it is lit up in the evening, and I am particularly fond of the marble bathroom in one of the master suites, which has an intimate scale and beautiful, filtered natural light. The Italian glass kitchen from Valcucine is also remarkable, both for its elegance and its precise engineering.

Q: Aside from a couple of really dramatic Italian light fixtures, reputedly made from recycled Ferrari headlights, that were too big to fit into the elevators and had to be craned into the 17th-floor condo, the space is pretty austere. What guided your choice of materials?

A: The owner wanted materials that created drama in the large open spaces, but were healthy and easy to clean. The living, dining and kitchen floors are very large-format porcelain (2 feet by 4 feet) that combine with the white walls to give these spaces a lovely abstract feeling. This was particularly effective when contrasted with the eclectic art and antiques collection. The rest of the floors are smoked black ash in a herringbone pattern that are richer and more intimate for the informal living spaces and the bedrooms. We also used glass guardrails and etched-glass doors throughout to continue the themes of openness and light.

Q: Were there specific art objects that helped guide the design?

A: While the space needed to house a large art and antiques collection, it was designed as a flexible display space. Horst loved to tinker with the placement of different pieces throughout the space, so we reinforced all the walls to hang art and designed the light to be easily reconfigured to highlight different paintings and objects.

Q: Now that it's finished, is there anything you'd do differently?

A: It's hard to say, since the space was designed around the needs and wishes of the clients. If I were living there, I might add another bedroom suite, which could certainly be accommodated within the current space.

Q: Was the abundance of space a help or a hindrance?

A: It's wonderful to have enough space that not every inch of it needs to be planned or furnished. There is a real sense of openness that comes with the ability to move around furniture freely and have enough space for guests to meander during an event. This open space is also ideal for sculpture or other art objects that want to be seen in the round.

Notable features

• 12,000 square feet on two levels.

• Three bedrooms, including two master suites, each with their own laundry, and five bathrooms.

• A private elevator to the unit, and an elevator within the unit.

• All-glass Valcucine kitchen.

• A mud room with laundry and a dog-washing station.

• Eight parking spaces.

• Several patios and terraces.

Barry Berg/Chad Larsen of Coldwell Banker Burnet have the listing, 612-925-8411.

Jim Buchta • 612-673-7376