CLINTON HILL Home to Pratt Institute, Brooklyn's Clinton Hill was once thought of as a get-away for well-to-do professionals.Today, exquisite mansions still populate the streets along side of the grand Italian Renessiance Brownstones and more modest carriage houses. Boundaries: Park Avenue on the north to Atlantic Avenue on the south. Vanderbilt Avenue on the west to Classon Avenue on the east. Subway access: G, A