From the center of Ubud, travel south on Hanoman Street towards Denpasar. Pass the Pertamina petrol station on your left and continue until the road dips down and curves left. Continue to the first intersection in Lotunduh, and turn left. (You will see a green sign, direction Mas/Goa Gajah before the intersection) 200m on the right is a driveway lined with tall green bamboo.
From here it is scooter or walking access only.
Cross over the bridge and follow the path about 180m along the river all the way to the end.