there is not much marking the tunnel, you will pass a bridge and it will be on your left. it has not rained for a while so the stream crossing shouldnt be bad. the road leading to the tunnel is gravel. here is a google map with it marked http://maps.google.com/maps?f=d&source=s_d&saddr=Columbus,+OH&daddr=39.307842,-82.323285&geocode=FVjCYQId9okN-ylx3pC5wYk4iDEztbHP-GYy5A%3BFULKVwIdq9gX-w&hl=en&mra=ls&sll=39.311756,-82.331371&sspn=0.012518,0.021586&ie=UTF8&ll=39.560177,-82.53891&spn=0.798293,1.381531&t=h&z=10