Northeast of Newark, the Middle Run Natural Area County Park has a 10 mile network of wooded singletracks. These trails are a solid middle of the week middle distance cross-country workout and a great training ground for new bikers.
To reach the mountain biking trailhead from Newark, follow SR273 as it turns into Main Street and at the corner of Main Street and North Chapel Take a right (Space II pizza on the corner, excellent place to stop for a bite). North Chapel becomes Paper Mill Road and you stay on Paper Mill for about a mile or two. When you see the MBNA building on your left and a large gas station on your right turn right at the left. The first street on your left dead ends at the tristate bird refuge (Middle Run).
When parked in the gravel lot at the main building, all the trails should be apparent. Note, you will have to mountain bike ride through streams to get to the good trails so be prepared to get wet. To reach the best trail, take the trail adjacent to the corn field down the hill and turn right at the bottom. Go across the stream and follow this trail for about 100 hundred meters and then take trail to the right. To reach the other trails, on the way in you passed the sign for the bird refuge on the right of the road and directly in front of it was a trail going off to the right. Take this singletrack and it should end in a large field. Go to the left on the field and there should be an entrance into the woods about a quarter of a mile. This trail connects to the other main trails.
Overall, Middle Run Natural Area is the 5th most popular mountain bike trail of all 5 mountain biking rides in Delaware.