Toronto's skyline is transforming at a blink-and-you'll-miss-it pace, and another titan of a tower is quickly making its presence known just across the street from Union Station.

Following the successful 49-storey first phase of the CIBC Square office complex completed at 81 Bay Street in 2021, a slightly taller 50-storey sibling tower is quickly on the rise just north of the rail corridor at 141 Bay Street—currently the tallest office tower under construction in Canada.

The enormous office complex from developers Ivanhoé Cambridge and Hines effectively doubles down on the first tower, boasting a matching design from U.K.-based architects WilkinsonEyre working alongside local firm Adamson Associates.

At a height of 241.4 metres (792 feet), the second tower at CIBC Square is the sixth tallest building under construction in the country and the tallest office building rising anywhere from coast to coast to coast.

Of the five buildings under construction in Canada that will stand taller, all are residential, and four are located in downtown Toronto – the lone exception being the M3 tower in Mississauga.

If completed today, CIBC Square's second phase would stand as Canada's eight-tallest building overall.

Rendering of 141 Bay Street, with the completed first phase tower on the right. Image/2015 DBOX

Construction for the second phase closely follows the method used for the first tower, with a central concrete elevator core gradually surrounded by a steel-framed skeleton for the office floorplates.

While this is the standard method of office construction around the world, it is still somewhat rare to see in a condo-obsessed Toronto, where reinforced concrete structures are the norm.

The steel frame now rises above the tower's 20th floor, while the concrete core soars ahead.

As more structural steel rises around the core, the tower's distinctive diamond-patterned facades have become more apparent along with the tower floorplates' east-west orientation — a 90-degree pivot of the first phase.

These levels are now being gradually enclosed in the same reflective blue curtainwall glazing and patterned lighting setup that has made the complex's first phase a smash-hit addition to the Toronto skyline.

The tower's completion will come with an expansion of the elevated park bridging the rail corridor, and create a new southerly extension of the Financial District bridging over the train tracks.

Like the first tower, 141 Bay Street will include its own pedestrian bridge over Bay, linking the complex with Union Station to the west. That bridge is already well under construction.