Take a bike tour at Lighthouse Bikes! They offer two and three-hour bicycle tours that visit area lighthouses and share local natural and historical information about the area. The three hour tour comes with an option to buy a delicious lobster roll at the famous "BITE INTO MAINE" food truck at the Portland Headlight. Really beautiful ride with incredibly friendly staff. You can also just rent bikes there.
They are located 1 1/2 mies from the cruise ship terminal-a quick walk or Uber!
Check out their website lighthousebikesportland.com