Complex sentence: Dr. Holbrook's Military School was a military academy and boarding school for boys located on Briar Cliff, which overlooked the Hudson River near Sing Sing (now Ossining), New York.
Split into simpler sentences: Dr. Holbrook's Military School was a military academy and boarding school for boys. The school was located on Briar Cliff, which overlooked the Hudson River near Sing Sing (now Ossining), New York.