As soon as you get off Rt. 6, you'll hit 149 at the stop sign at the end of the offramp. If you hop on the service road right there which is lined up with the powelines you can see, there is a parking lot and trailhead about 50 yards from the highway. Go around the gate and down the dirt road about 100 feet and hop into the woods on a little trail to the left.
A closer place to start from Rt 6, yes, but a little tough for a newbee..it's like in the middle of the mapped loop (instant good riding, though). A lot of locals start here, it's I just can't stand that parking lot. I Hate: the highway feedback, the frigg'n dogsh*t, busted bottles, wet sh*trags, rubbers, stink'n smell & the powlines humming above. I used to start there...but after seeing so much glass on the ground (car windows?), I just drive a couple of miles further and use one of the several other trialheads. The Main, I mentioned is a nice place to start for the first timer, sure its flat for a mile or so, but hey, its sweet singletrack. For me at least, it's a nice place to gear up, warm up...then geardown & chill with a post brew. It's all about riding, for sure man, but that powerline parking lot makes me sick to think about what pigs humans can be. Last year, the illegal dumpings were gross!
I actually made the first GPS map of TOT for the Town of Barnstable about 10 years ago when it became clear that the local secret was out and it was going to be mapped anyway... It took about 10 hours to loop all around.
That is very cool!
One good thing about TOT is the powerlines - you can always get back to the parking lot quick if you can find your way to the power lines. Have fun.