Camden, Maine is 90 miles north of Portland on the coast, and it is the small-town New England experience most people go looking for in Bar Harbor and do not find. Bar Harbor is fine. It is also overrun with tour buses by 10am from June to September. Camden is quieter, better food, more locals, one specific great bookshop and no fudge shops. This ratio matters.
Stay at the Whitehall for a night if the budget allows. Walk up Mount Battie in the morning for the harbour view that Millay wrote about. Eat lobster at Peter Ott’s (touristy but good) or at Long Grain (Thai food you would not expect in a Maine coastal town, run by a chef who moved back from New York). Browse The Owl and Turtle, which is one of the best independent bookshops in Maine.
What Camden has that Bar Harbor does not: a working harbor. The boats are lobster boats, not tourist boats. In September the schooners come in for the classic weekend and the whole town smells like pine and diesel. In October the leaves turn and the light is the light of every Maine painting you have ever seen. Two nights is exactly enough. Three, if you like sitting.