A friends daughter gave me the following info:
"things to do in Portland :
breweries: if you like to imbibe or enjoy brewed beverages I recommend checking out some of the local breweries ie Allagash, shipyard, urban farm fermentory (all accessible either by walking or uber). or pay $70/each for a few hours guided tour that includes transportation, food, beverage samples and a commemorative bag
lighthouses: since you are carless I recommend a tour such as the “lighthouse lovers” boat tour by portland discovery nearby to where the cruise ship docks or tenders and there are directions on their website $19/each
food/foodies: Portland has an awesome and evolving food scene. clearly lobster and seafood are big! you can explore fan faves on your own which are nearby to the port, such as Duckfat, Holy Donut, Eventide Oyster Co, or Portland Lobster Co. or you could pay about $70/ each for a guided tour. they offer culinary walking tours, lunchtime lobster crawl or a harbor cruise and lobster picnic.
sightseeing: if you’d like to get a good tour of Portland I recommend Portland Fire Engine Co. They offer a 50 minute guided sightseeing tour aboard an old-fashioned fire engine truck. they hit all the local highlights and is a good deal at $24/each. also the ride starts and ends right in the old port area on Commercial Street, so you can shop, eat and explore before or after your ride. here is info for cruise passengers from their website:
active: if you are craving something active to do, Portland offers a beautiful eastern promenade with pathways to walk and a beach to enjoy can be reached by uber. or it would be fun to take the ferry over to peaks island from the casco bay lines/ for $7.70/each round trip and rent a sea kayak or bike on the island to explore. a recommendation for kayaks is maine island kayak they offer guided kayak tours of a half day tour to see lighthouses, islands, and wildlife for $65/each for a tandem kayak or a sunset tour for $65/each for a tandem kayak. or you could rent bikes and helmets from brads bike rental and repair.. for about $10/each/hour to explore the island. people rave about the sights and the eerie historical location of BatterySteelee, a WWII era military fortification on the island. both rental shops are walking distance from the ferry.
art: as Skylar said it would be awesome to enjoy a paint session at muse paint bar where they work you can visit the website to see if any sessions are going on the day(s) you are here and book them if you want. The studio is walking distance from the docks, and is located on the same street- Commercial Street. if you would like to check out the local art museum, admission is $15/each for adults or there is a deal on groupon (free app) for 2 adults admissions for $15.50 instead!"
We are doing Bar Harbor by air with Scenic Tours of Acadia. This is something different that will always stay with us!
Hope the information helps! Enjoy your trip!