Some people hang works of art in their homes to give them something beautiful to look at. Robert Caine has no need for priceless paintings. He has a masterpiece right outside his windows.

Caine and his wife, Linda, were living in another part of the Watergate complex when two units with Potomac River views came available.

“The ability to combine the two was irresistible,” he said.

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The sweeping views of the river, Roosevelt Island, the Key Bridge and Georgetown informed every step of their transformation of the two units into one. First and foremost, each room needed to have an unobstructed vantage point of the spectacular sunsets.

“Our parameter was really pretty simple, and I think you can see it as you go through the apartment — it was simply the view,” Caine said. “Every single major room faces the river, even the kitchen. The butler’s pantry sees the river. Everything sees the river. The bathtub sees the river.”

The tricky part was merging two of everything. An extra bedroom or living room is one thing, but what do you do with a second kitchen?

Because they enjoy entertaining, the Caines turned it into a butler’s pantry that can function as a place to serve drinks or a caterer’s staging area. The advantage of having two entrances is that the caterer can come and go from the entrance that leads to the kitchen while guests are arriving through the main doorway.

The renovation is seamless. It is difficult to spot where one unit ended and the other began. Where a wall once separated the two dwellings, a folding door acts as a movable barrier between the dining area and the media room. The new open layout offers plenty of room for entertaining. The entertaining space extends to the balcony, which stretches the length of the apartment.

Before retiring, Caine was an eye surgeon, and he brought the same meticulousness to the renovation that he did to his work. Plus, he and Linda had renovated several previous homes and knew what they liked and didn’t like.

“I’m used to working in tenths of millimeters,” Caine said. “I’m just unforgiving when it comes to details.”

It’s the details that set this home apart, from the cove lighting to the Swarovski crystals sparkling above the dining room table, to the Roberto Cavalli porcelain tile imported from Italy on the floors. A secret panel next to the gas fireplace that opens to the master-suite sitting room is another trick they carried over from a previous home.

The monthly co-op fee of $6,401.11 includes property taxes, utilities, Internet, cable, maintenance and Watergate amenities such as a 24-hour concierge service, doorman service, a saltwater outdoor pool, a fitness center and two underground parking spots.

The three-bedroom, five-bathroom, 3,007-square-foot apartment is listed at $4 million.

Listing agent: Gigi Winston, Winston Real Estate