I've visited the 9/11 Memorial a couple of times so skipped it on this trip; One World Trade Center (ie Freedom Tower) is still jaw-dropping as the tallest building in the Western Hemisphere (the same architect designed Willis Tower and Burj Khalifa)
We tried to book scuba and snorkeling trips to Molokini and Lanai but everything was booked solid for the next 2 months; rental cars and hotels/condos sold out with international travel for Americans still largely banned
The Cooper-Frost-Austin House, built in 1681, is the oldest house in Cambridge; the city of 116,000, home to Harvard and MIT, has 57% of its residents possessing at least a bachelor's degree