Take Route 3 North from Nashua up to Route 93. Get off Route 93 at exit 12 (South Main Street). About 500 yards up, turn left onto Rockingham Street, then turn right onto South Street. The field is about 1/2 up on the left.
Alternately, you can take Exit 1 off Route 89 (South Street/Logging Hill Road). Turn left at the end of the exit ramp and follow South Street for a little over 1 mile and the field will be on your left.