Callahan State Park Framingham, MA
Callahan is a great place to put in some miles after work or if you don't have a ton of time. Fun trails that you can hammer over. Definitely more of a cross country style trail system, so don't expect anything terribly technical and definitely no jumps / stunts.
Callahan is a great place if you want to get in a quick spin after work. It is definitely not a weekend destination ride. Mainly cross country trails with some fireroads mixed in. The trails are split into two distinct sections. North and South of Edmands Rd.
The south side is mainly made up of doubletrack trails with a some sections of singletrack mixed in. This side is also where you will run into a lot of walkers, dogs and sometimes horses. Nothing terribly technical on this side of the park. With the Hawk trail being one of the funner trails going from south to north. If you explore enough you will find some fun, so explore away, it is almost impossible to get lost on this side.
The north side of the trails is interesting. It starts with one hell of a technical climb when crossing over from the south side. The roots and rocks on the north side are a plenty. Unfortunately, the trails on the north side are horribly marked, yes, there are some blue markers but they often just end or lead you to a dead end. Luckily, there are park signs posted at times to help you out. The north side is definitely more technical and has a ton of climbing, so only venture over if you have some time. If you do venture over, I highly recommend hitting the Meadow trail. It isn't especially difficult, but there is something about hammering down the singletrack around the meadow that is especially fun. It is also a great place to stop and take a break while eating a bar on one of the benches over looking the meadow.
The south entrance seems to be where everyone parks, so it can be full and hard to park in at times. The parking lot is directly across from Millwood Farms Golf Club on Millwood St [42.320713,-71.463146].
The north entrance is rarely used and always has parking. It is a bit harder to find and starts in a weird location on the trails. It it located near 241 Broadmeadow St, Marlborough, MA 01752 [42.33876, -71.50048].
There is also a small parking lot on Edmands Rd. just past Stearn's Organic Farm.