The "park" uses an old elevated railroad line that has been long abandoned and weed infested. As they say, the most sustainable design is one that re-uses what is existing and this is exactly what they did. Look at the narrow gaps of the paving at the left. Some still contain the steel rails of the old railroad. On the Highline you can stroll 3 floors above the street level through the west side of the city near the Hudson River -- a little removed from the hustle and bustle below. There are elevators so the park is accessible for wheelchair visitors.