From Gračac you go north the D1 street to Zagreb until the restaurant Zagi in Deringaj. There you have to take the unpaved road to the left or you follow the walking track over the hills (walking distance is about 20 minutes from the restaurant, here is the GPS track https://www.openstreetmap.org/user/rasos/traces/1766744).
Coming with train
Gračac has a train station with a few trains per day and one in the night from Split and Zagreb. The train station is 10 km away, so call 00 385 95 81 444 15 for pick up.
Coming with airoplane
The closest airport is Zadar.
Coming with car or bike
from Zagreb direction: pass Zagi restaurant and drive for another kilometre. You will see a bus stop on your left and a unpaved road that goes from the beginning fo that bus stop. Take that for 400 meters, cross the wooden bridge and another 50 meters turn left into the MMK field.
From Gračac: go direction Zagreb, pass by Lost Theory festival therein on your left, pass by entrance to Deringaj village on your left, drive for few kilometres until old bus stop. At the end of bus stop there is unpaved road to your right. Take that for 400 meters, cross the wooden bridge and another 50 meters turn left into the MMK field.