The 34-unit Acqua is the first project designed by Mr. Viñoly in his home country. Mr. Viñoly is the architect behind Jazz at Lincoln Center, the Brooklyn Children’s Museum and the Tokyo International Forum.

The tiered, glass-walled Acqua, which is in its final stages of construction, is about 50 percent sold, according to Flor Vrljicak, a spokeswoman for the project. Eighty percent of the buyers are from Europe, she says. Prices start at $980,000 (743,000 euro).

The recently sold four-bedroom penthouse covers 18,500 square feet (about 1,719 square meters), with an 800-square-foot (74-square-meter) master suite and ocean views on three sides. It also includes a private swimming pool, home theater, wine cellar and servant quarters.

Ms. Vrljicak declined to offer any details about the Swiss buyer, other than to say the penthouse was purchased as a second home.

Punta del Este, often referred to as the Riviera of Uruguay, is a high-end resort city popular with jet setters from Argentina and Europe.