1. Salem Witch Trials: On August 20, 1692, Martha Carrier was hanged in Salem for witchcraft, making her one of the last individuals to be executed in the infamous trials that took place in the Massachusetts town.

2. Boston Tea Party: On August 20, 1775, a group of American colonists in Boston held a mock funeral for a loyalist judge and then proceeded to dump tea into the harbor, an act that would ultimately lead to the Boston Tea Party and the American Revolution.

3. Birth of H.P. Lovecraft: On August 20, 1890, legendary horror writer H.P. Lovecraft was born in Providence, Rhode Island, just a short distance from the Massachusetts border. Lovecraft's Cthulhu Mythos and other works remain hugely influential in the horror genre to this day.

4. First Public Park: On August 20, 1830, the city of Boston officially opened the gates to the Boston Common, becoming the first public park in the United States. Today, the park covers 50 acres and is a popular destination for visitors and locals alike.

5. Harvard Medical School Founded: On August 20, 1782, Harvard Medical School was founded in Boston, becoming the third medical school in the United States. Over the years, the school has produced numerous notable physicians and researchers, including Oliver Wendell Holmes Sr. and Dr. Paul Farmer.