Mystic Aquarium is one of the reasons Mystic works as more than a quick highway stop. The village is small, so even the major attractions feel tied to the river, the bridge, and the working-waterfront history around them.
Summer is busy and ticketed sites can be expensive, so choose what actually interests you. A good Mystic day balances one major attraction with a walk downtown, time by the water, and perhaps a side trip to Noank or Stonington when the crowds thicken.