One of the most peaceful places in Boston to read. I prefer sitting on the bridge off to the left of the main gate. You'll hear more birds and insects than cars.
A part of the Arboretum that's less crowded and offers awesome city views. There are also trails along the train tracks where the pups can be off-leash.
Sit on the benches by the pond during the day with a good book. And enjoy a lovely picnic at night with some hot tea. The public garden is truly one of the most beautiful places in Boston.
Go to the fountain open area in the library and check out the marble sculptures and the art galleries in the library.
