This home takes window shopping to another level.

In a sea of townhouses, one residence on Manhattan’s Upper East Side has charmingly refused to blend in — and now it’s looking for a new steward bold enough to match its energy.

The so-called “Bubble House,” a 1969 modernist townhouse at 251 E. 71st St., has hit the market for the first time in half a century, asking $5.75 million, Curbed first reported. The house earned its moniker from its bubbly windows and whimsical aura.

With its stucco façade pierced by convex “ovoid” oval windows — some of which rotate open like space-age portholes — the four-story home has long been a spectacle on its quiet Lenox Hill block.

“People walk by and they can’t help but stop and stare,” Richard Pretsfelder, one of the home’s listing reps with Leslie J. Garfield, told The Post. “Unlike almost any house I’ve ever heard of, people would actually stop and knock on the door sometimes — which is not particularly common in New York.”

Originally built as a traditional brownstone in the 19th century, the building underwent a radical transformation in 1969 under architect Maurice Medcalfe, who also lived in the home during its reinvention.

His reimagining of the property coincided with the height of both space-age aesthetics and modernist experimentation. But there’s more than meets the eye

Added Pretsfelder, “there’s also like a nautical influence, a sort of a porthole element to the whole thing.”

The timing, he added, made all the difference. “It is less likely to have been done in a different era.”

The 4,736-square-foot residence includes four bedrooms, five bathrooms and an office on the garden level.

Though the exterior may be avant-garde, the interior layout is conventional by comparison, with sunlit rooms and a flexible floorplan.

A hot tub was recently removed in preparation for sale, and while the interior remains largely functional, “it just requires work,” Pretsfelder said. “Someone’s going to come in and really do a full renovation down to the studs and make it their own. That may include the façades or not.”

The house has had only a handful of owners and was most recently occupied by Rabbi Arthur Schneier, the longtime leader of Park East Synagogue, who purchased it in 1974.

Despite its architectural uniqueness, the home is not landmarked, which opens the door to potential alterations — something that has stirred local curiosity, if not concern.

“That is the multi-million dollar question, isn’t it?” Pretsfelder said of whether a buyer might preserve the façade. “I think they’re probably looking to maximize their dollars … But ultimately it’ll go to the highest bidder.”

Still, New York native Pretsfelder hopes its next chapter respects its legacy.

“Anybody who grew up in the city has seen it around for the last 50 years,” he said. “I’m sure they’d [the current owners] love to see it retained in its current format. But that remains to be seen. As with most pieces of real estate, it’ll be the dollars that do the talking.”

This listing may be what lures design lovers, collectors, or creative buyers in search of something no renovation — or zoning board — can replicate.

“It’s just an iconic part of the neighborhood,” Pretsfelder said.