On June 16th afternoon, we visited Grand Central Terminal again. This time, with a professional architecture tour guide, we explore the neighborhood. At the end of the tour, we were standing on 45th street between Park avenue and Vanderbilt avenue. We were surrounded by two buildings: Helmsley Building and MetLife building.
What I found interesting was the expansion joints in the middle of streets as shown in the picture below.

Those joints are usually used for the structure of a bridge. Yes we were technically standing on a huge bridge. The guide explained that these were the bridges above the park avenue train tunnels, which used to be open to the grand as shown in the picture below.

Photo@ Douglas Feiden, Rising Above the Rails at Hudson Yards, The Wall Street Journal http://www.wsj.com/articles/SB10001424127887323368704578592141407884714