A must-see are the Trelis lights at the Christopher Columbus Park in the North End of Boston:
The Upside Down Trees are what I term the "Holiday Hidden Gem" in Boston's Liberty Hotel. This yearly display of decorated and lit trees is not to be missed:
At Faneuil Hall, you can see Blink, a music and light show, nightly (but whatever you do, don't "blink!"):
Hope you enjoy finding all things Festive and Bright in Beantown!