Bike trails north of Boston

The Minuteman, on a warm weekend day, is a bit of a mess, especially the further east you go. The section west of Arlington is a bit better since there aren't as many grade crossings so less access (there's about 2 miles straight from Arlington with no roads) and there are only a couple of streets between Arlington and Lexington. West of Lexington is usually less crowded, too.

If you go to Google Maps and click on the bicycling layer (menu--> bicycling) you can show other bike paths. Much of Boston once had a web of rail lines, many of which are redundant enough that they probably shouldn't be used for anything but paths. (The Minuteman is successful as a bike path, but if it were a Commuter Rail line—as it was until the late '70s—you could get from Arlington to North Station in 18 minutes: try doing that today at rush hour!)

It's sort of a shame the state has no concerted program to provide for path conversion, it's sort of based on where there's interest and who can get a little money. They came pretty close to greenlighting the Wayside Rail Trail from Waltham to 495 back in the late '90s until Weston voted against it (because apparently ne'er-do-wells from Waltham were going to come and steal television sets on the bike path, or something) and while trail backers vowed to push on, the project lost momentum after that. (IOW: fuck Weston.)

The Bruce Freeman is probably the longest project north of the Pike right now: the portion in Chelmsford and Westford is complete and the rest to Sudbury is under construction (quite a bit open this fall, more in a few years). The Assabet River Rail Trail isn't too far behind (South Action to Marlborough). If ever built, the Wayside/Central Mass would connect these two. Further afield, the Nashua River Rail Trail runs 13 miles from Ayer to Nashua and is probably very nice. That may be your best bet for a nice quiet trail, and it's under an hour from Boston, and easily accessible by train from Ayer.

There are several paths from Danvers on north, but they are generally pretty fragmented and unpaved.

TL;DR: Best bet right now Nashua River Rail Trail, as of this fall, Bruce Freeman a good idea too.

If you want to avoid cars, this is your trail! Beautiful, too. May be a few jam ups while large turtles cross, but otherwise it is lovely. It also doesn't attract the slower or less experienced folk because it can be several miles between trail heads.

If you take it all the way into Nashua, it gets nuts, but the bulk of it is just plain lovely.