REMOVE

1. barriers
2. buildings (structures)
3. rubbish
4. Grand Coulee Dam (dam)

WHAT

1. Visual Works (hierarchy n … (1)
2. artists (visual artists) (1)
3. benches (furniture) (1)
4. branches (plant component … (1)

More 

WHERE

1. New York, New York (1)

WHEN

1. 1964 (1)
2. ca. 1964 (1)