Crews top off Boston’s newest skyscraper, One Dalton

Construction workers signed a wall in the basement of One Dalton.David L. Ryan/Globe Staff

The topping off of the tallest new building in Boston in 40 years started out 742 feet below, at ground level. There construction workers, members of the development team, and local officials gathered to celebrate a milestone in the construction of the Four Seasons One Dalton in the Back Bay Tuesday. They then rode up construction elevators for a look around.

When the 61-story hotel-and-condominium building is finished next year, the penthouses — with stratospheric prices of $40 million — will be the highest place you can live in all of Boston.

If that’s your bag, and your price range, move fast, though. A spokeswoman for developer Carpenter & Co. said a number of units are already under contract, and the company expects all 160 condos to be sold by the time the building opens.

Developer Dick Friedman and Mayor Martin Walsh surveyed the view from the 59th floor.David L. Ryan/Globe Staff

Abigail Summerville took a photo out the 59th floor window of One Dalton.David L. Ryan/Globe Staff

The top of One Dalton provides a spectacular view of the Back Bay and the Boston skyline.David L. Ryan/Globe Staff

Construction workers found shade during the topping off ceremony at the Christian Science Church complex.David L. Ryan/Globe Staff