You could say that the Seaport—targeted years ago as the Innovation District and as a hub for techies—has all the right angles. But that’s not necessarily a good thing. The early additions to its skyline shaped up to be pretty, well, square. A new exception is 121 Seaport Blvd., where a cylindrical tower sits.

“A circle is the most efficient shape there is,” says Charley Leatherbee of Skanska USA, the building’s developer. Its elliptical form and position—turned 45 degrees from the street—let the tower get more light, less wind resistance and use less building materials than traditional boxy high-rises, says architect Phil Casey of CBT. But the oval design is also striking and, surprisingly, easygoing.

ROUND ABOUT: The shape of 121 Seaport Blvd. helped it earn a LEED Platinum rating, the industry’s equivalent of an A-plus for efficiency.

OUTSIDE IN: The lobby is glassy and grand, but giant panels of paldao wood that line the ceiling and curved walls lend some warmth.

UP-LIFTED: The elevators calculate the most efficient routes, making the building as high-tech as its occupants: software-maker PTC and Alexion Pharmaceuticals.

Even from below, the high-rise doesn’t appear as tall as its 18 stories. That’s because it’s 20 feet slimmer at the bottom than at the top. Upon entering, the lobby feels vast. The hall blurs the line between inside and out with a 50-foot-high wall of glass at the entrance and large S-shaped benches resembling those of a city park. At the building’s top, there’s a roof deck that’s guarded by a massive glass parapet, protecting visitors while giving them near panoramic views.

All this lets 121 Seaport defy much of what it means to be a corporate high-rise. In fact, it’s like a round peg in a square hole.

121 Seaport 121 Seaport Blvd., Boston 121seaport.com