The marked trails are mostly wide fire roads that are predictably boring for mountain bikes, but there is tons of singletrack off the beaten path. The best trails hug the edge of the Assabet river (just look for them), the north-east corner, and also in the center. The center of the property has a decent hill with four trails that go straight to the top - these would be challenging for a beginner (long, sustained climbs). One of these four trails I'd call "downhill only" since it's very steep and rocky (but fun!). If you just ride the fire road perimeter, it's only about 4 mostly flat miles, but if you explore the plethora of singletrack you can go as long and as hard as you like - just bring your GPS so you don't get lost. You'll find sufficient cell phone signals throughout the property if you're using an Internet map.