Is bike registered?
If so park in Urbenville and take Boomi Ck Rd [ Clarance way ] for a short distance east from town then turn right into Connells Rd and keep fading left [ don't take Smiths Rd ] good fun bit this.
You will end on South Yabbra Rd , left takes you back on Clarance Way ,[ bitumen], turn left then right into North Yabbra Rd and get lost in there [ can end up on Summerland way if you go NE]. [ Bulk roads in there , forestry and Nat Pk ] turning right at South Yabbra Rd takes you way down into Yabbra National Pk.
Watch out for bikes coming the other way cause it's a popular place.
Unregistered could be a worry.
Cheers.