Located near the Stamford-Greenwich-Westover border, the 180 acre Mianus River Park has a 10 mile network of trails shared by hikers and bikers along the Mianus River. These trails are rocky and wooded. Plus there are fire roads and carriage roads with some climbs. The Mianus River runs the east edge of the park, so dont worry too much about getting lost.
To reach the mountain biking trailhead from US95, use take Exit 5. Take a right heading east on to the Post Road (SR 1). After 0.25 miles at the first light, take a left onto Sound Beach Avenue. Sound Beach ends in about 1/2 mile at a Stop sign. Take a right on to Sheephill Road. Go about 1/2 mile until Sheephill ends at a Stop sign. Take a left on Palmer Hill. Go over the Bridge and take a left onto Valley. In about 100 yards, take a right onto Cognewaugh. Follow Cognewaugh about 1.5 miles until until you see a small dirt parking lot on the right. This is the parks entrance.
Overall, Mianus River Park is the 4th most popular mountain bike trail of all 16 mountain biking rides in Connecticut.