The owners of a Boston office tower known for its slender base which expands into a hexagonal facade plans to refresh the building with a new glass-enclosed lobby wrapping around the bottom three floors.

Proposed updates to 175 Federal St. include 12,000 square feet of new retail and restaurant space including a raised public observation platform overlooking the Rose Fitzgerald Kennedy. The entrance and lobby would move to the corner of Purchase and Summer streets.

“The classic challenge for a lot of buildings in Boston is: where is your front door?” said Haril Pandya, a principal at CBT Architects. “Right now, the front door feels like a loading dock, and it was a collision of trucks and people.”

Approximately 20,000 pedestrians travel daily past the building, which sits in a major corridor connecting South Station to the Financial District, Pandya said.

The removal of the elevated Central Artery continues to influence commercial landlords’ capital improvements on the eastern end of the Financial District. In 2016, Oxford Properties Group relocated the main entrance of its 125 Summer St. office tower to face the Greenway.

“We thought 175 Federal St. should follow suit. It was sort of the dark swan on the Greenway,” Pandya said.

The proposed changes are subject to small project review by the Boston Planning & Development Agency, and approval by the Boston Civic Design Commission.

The 227,365-square-foot tower, formerly known as the Fiduciary Trust building, was designed by the well-known modernist architectural firm, The Architects Collaborative of Cambridge, and developed by Beacon Cos. and Carpenter & Co. in 1977. The narrow base was required because of MBTA tunnels and utilities that run beneath the site.

German real estate investor Deka Immobilien Investment bought the property in 2016 for $139 million.