Plenty of bike trails are available for a Maine biking expedition

45 miles of historic carriage roads donated by the Rockefeller family weave around the mountains and valleys through the heart of Acadia National Park. The roads have crushed rock surfaces perfect for bicycling. Cyclists share the carriage roads with horses and pedestrians, enjoying sweeping vistas and close-up views of one of America’s most breathtaking landscapes.
Click here for a Trail Map (PDF)

The Down East Sunrise Trail is preserving 85 miles of rail corridor for future use by snowmobilers, ATV-ers, pedestrians, bicyclists, cross country skiers, equestrians and walkers. Now, 30 miles of multi-use trail is open for permanent year-round use from Machias, east to Ayers Junction (except for mud season). The remainder of the trail from Machias west to Washington Junction will be opened in phases.
Trail map.

The National East Coast Greenway is a 3,000-mile biking trail connecting Calais, Maine, to Key West, Florida. The greenway route in Maine is about 400 miles. Here are some of the greeway loops. All rides below are described as moderate to difficult, for intermediate and experienced cyclists.
Eastern Trail from Kittery to South Portland. 68 miles. The Eastern Trail connects Bug Light Park in South Portland with Strawbery Banke in Portsmouth, NH.
Casco Bay from South Portland to Brunswick. 35 miles. This pleasant ride takes cyclists from Portland’s waterfront to nearby suburban towns, including Falmouth, Yarmouth, Freeport and Brunswick, and the Maine coastline.
Details of trails .

Plans call for the Mountain Division Trail to ultimately cover 52 miles between Fryeburg and Portland. Two sections of the trail are open now. A 6-mile segment between Standish and South Windham provides a gently rolling ride in the Sebago Lake watershed area, northwest of Portland. The second leg, in Fryeburg, begins not far from the Maine–New Hampshire border and travels 4 miles along the railroad right-of-way. To get onto the southern segment, start from the western trailhead at Johnson Field in Standish. To get onto the shorter northern segment, start from the Maine State Visitor Information Center at 97 Main Street in Fryeburg. The paved trail ends near the small regional airport and the Brownfield town line.

This 1-mile trail is a flat, paved surface through the Bayside and East Bayside neighborhoods. It extends at the south end from Elm Street between Somerset Street and Marginal Way and parallels Marginal Way, linking with the East Promenade and the Back Cove Trails near the highway overpass where Route 1 crosses Back Cove. There are several benches and three water fountains. Trail is good for walkers, runners, and bicyclists.