The MTB Scene in Maine is absolutely blowing up right now and even outside of a huge MTB riding destination like CV, there is still an abundance of riding available.
For the greater Portland area, I would not recommend Bradbury. Bradbury is one of the premier MTB destinations in the area but not much has changed their in the last 15 years other than a lot more roots becoming exposed and things getting a bit more technical. Portland is a great hub for MTB riding, especially if they are into the food/brewery thing (there's plenty of that too). I'd recommend that they download the Trailforks App to their phone and seek out a few spots in Falmouth ( Trailheads are 20 min drive from downtown Portland).
Blackstrap is probably the most popular and fun place to ride (and coincidentally has the most vert out of anywhere within a good size radius). Blackstrap is full of a mix of fun technical climbing and technical & flowy descents. Park at either the Hurricane Road trailhead or the Hadlock Road Trailhead. Whatever you do, don't let them start at the Blackstrap Preserve trailhead (very hard to ride hiking trails - not fun).
Here is our guide on riding in the Greater Portland Area:
https://www.allspeed.com/articles/falmo ... -pg183.htmhttps://www.allspeed.com/articles/cape- ... -pg185.htmhttps://www.allspeed.com/articles/gorha ... -pg186.htmhttps://www.allspeed.com/articles/portl ... -pg184.htmhttps://www.allspeed.com/articles/yarmo ... -pg188.htmSend them into Allspeed and we can help them out with showing them some good routing to make sure they get the most out of their visits.
Also, we do group rides on Monday and Thursday nights and would be happy to have them join in. Tell them to drop me a line chris a t allspeed d0t com or call the shop at 207.878.8741. We'd be happy to help them out.