Gulf Hagas is an 8-mile loop trail in the 100 Mile Wilderness. It may possibly be the hardest blue blaze on the AT, especially considering there’s only a couple hundred feet of elevation.
Gulf Hagas is a slate canyon, filled with waterfalls and narrow walls and innumerable overlooks. You can’t camp there, however, but if you start the day from Gulf Hagas Lean To (or Sidney Tappan campsite) you should be able to hike the Gulf and reach the campsite at East Chairback Pond - or stealth camp somewhere before.
There are other notables -
North Peak Trail, on Moxie Bald. Very short trail, great views.
Grafton Loop Trail - down by Baldpate. It would be slightly tricky to do the entire 30-mile loop without hiking extra AT miles, as the loop involves part of the AT. Some campsites on the trail, and of course the AT.
And then there’s the other half of Baxter - the northern half. Start up at Matagamon Gate, and hike down past the Traveler, South Turner, and take an easy trail up Katahdin, the Saddle Trail.
Going down Hunt will be a beach, though.
Kineo Kid