Today, six months after the design for Vessel was publicly unveiled, construction on Thomas Heatherwick’s otherworldly new urban landmark has officially begun at Hudson Yards on Manhattan’s far West Side.

The 150-foot-tall polished steel pavilion will anchor a five-acre public plaza and gardens, designed Nelson Byrd Woltz Landscape Architects, and will comprise 154 interconnecting flights of stairs, 2,500 steps, and 80 landings.

Expected to top out later this year and officially open in the fall of 2018, the copper-colored Vessel will be “pieced together like an incredible jigsaw puzzle,” said Heatherwick, from 75 individual parts fabricated by Cimolai S.p.A. in Monfalcone, Italy. Only the first 10 have arrived in New York so far, following 15 days at sea.

“As one of the most complex and ambitious pieces of steelwork ever made, the next months will provide a one-off opportunity to see a future extraordinary structure emerge for New York,” Heatherwick said.