Complex sentence: The neighborhood, loosely defined as bounded by Walnut, South, Front and 8th Streets, contains the largest concentration of original 18th-and early 19th-century architecture of any place in the United States.
Split into simpler sentences: The neighborhood, loosely defined as the area between Walnut, South, Front and 8th Streets. It contains the largest concentration of original 18th and early 19th century architecture of any place in the United States.