Try looking up 'sweet' in a couple of the excellent dictionaries here, and use your common sense.
Student or Learner
Does this "sweet" refer to "pure" or something?
gip86) Florence is known to the Italians as Firenze, which means "full of flowers."...Beyond the city is the whole sweet Valley of the Arno, glowing in a landscape of natural beauty and golden sunlight.
There were numerous definitions, and I couldn't help but conclude it's "satisfying or agreeable to the senses of the mind", considering the whole context.