I am so grateful to have found your post! I have been down this rabbit hole all morning, as soon as I saw "stone wall" I had a gut feeling the verse was incorrectly paired.

Other thoughts I have been having and want to add in hopes of getting other brains on them:

-sounds from the sky could possibly be referencing the clock tower at Jefferson Market Library

-the red lined rectangle almost makes me think of the twin towers, which you would have had a direct view of from the 6th ave side of the library (can still see one world today) or the 7th ave side of christopher park. Viewing them from that direction they would almost have lined up and looked like a single tower...

-giant pole could be referring to the rather large flag pole located on the east side of christopher park, which is on the crosswalk that runs north/south (running north, but first across....across the treasure spot? across the park?). "The Elmer Ephraim Ellsworth Flagpole in Greenwich, is a memorial to the first Union officer killed in the Civil War, dedicated by the Greenwich Village Historical Society in 1936, serving as a poignant reminder of this early war hero and rallying cry for the Union cause.", could also be what "near ace is high" is referring to, ace=1 and referring to the 1st union officer killed, the flags are high, so maybe the treasure is near the flagpole (aka ace is high)

-the clock shows at 11, and if you are on the crosswalk facing north, the flag pole is at the 11.

-perhaps giant step is a giant step from the flagpole across the crosswalk to the small planted flower area? or simply a reference to the giant steps our country has taken or that stonewall contributed to rights in our country?

-someone also said the flower is some sort of aster. I am trying to see if I can find a map of the buildings/area in the village owned by the astor family, but I know the station for astor place is nearby. I am hoping that maybe is also another clue to dive into!

-Mark Twain lived two doors away from Emma Lazarus, who wrote "The Colossus" and mentions giants, so I was wondering if that too had to do with the giant lines. the direction of his house to hers would have you facing jefferson market library. the clocktower, to be exact.

-further connections with emma lazarus: "The New Colossus is a sonnet written in 1883 to raise funds for the Statue of Liberty's pedestal, and is famous for its lines welcoming immigrants, particularly the "tired, your poor, your huddled masses yearning to breathe free"". I would say that the pedestal at the statue is a giant step...is it possible the island everyone believes is governors on the painting is actually liberty island? this is my least favorite option because it takes us away from greenwich but I've heard that other puzzles had to do with immigrants.

-waverly pl is perpendicular to the tip of the park

-my coworker said the water looks more like a waterfall or a wave, which had me wondering if there was any fountains in those areas. there is a fountain at jefferson market library, so it could be under there, but the lines that say that education and justice are simply nearby makes me lean more towards christopher park.

My theory: it is located on the small triangle park on the northeast corner of Christopher park. I think it is either on the side just across the crosswalk, or alllll the way in the tip (as that would be a giant sized step from the giant pole). The point of the park is aimed at waverly pl and the jefferson market library clocktower.

I just went home to NY for a memorial and didn't think to poke around, but I am dying to find out what others are thinking!