It is between Mandorim (Mandrem) and Morjim.
If you reach the lagoon at Mandorim then you've gone too far. Simplest way I've found to get there is to head for Morjim and take a right just before you hit the coast. It is sign posted.
I think you can also go through Morjim and keep heading up the coast.
If you try to get to it from the new main road then it gets tricky, lots of dirt tracks to navigate and no sign posts.