The newly opened High Line public park. More Photos >

A view along the newly opened High Line public park. More Photos »

Standing on a newly renovated stretch of an elevated promenade that was once a railway line for delivering cattle — surrounded by advocates, elected officials and architects who made the transformation happen — Mayor Michael R. Bloomberg cut a red ribbon on Monday morning to signify that the first phase of the High Line is finished and ready for strolling.

Calling the High Line, which opens to the public on Tuesday, “an extraordinary gift to our city’s future,” Mr. Bloomberg said, “Today we’re about to unwrap that gift.” He added, “It really does live up to its highest expectations.”