You can get Transdev buses out from Coimbra, but if you're not in your own car, a taxi is the best bet, as the buses are not what you might call over regular!
So, assuming that you're coming in your car, make your way to Brasfemes and then locate the Bombeiros. It's on the corrner of Rua Tapada and the main street (not given a name on the map, but indicated with arrows).
After that, it's plain sailing.
Turn right by the Bombeiros into Rua Tapada – there’s a farmácia opposite on the other corner. Keep going on this road, past the pink Junta de Freguesia building on your right, and keep bearing right around the bend into Rua do Lagartinho. Then the road straightens up and you come to a fork after a couple of hundred metres. Go left into Rua do Sardoal and it's the third house down on the left, before the orange house.
Rua do Sardoal 5, Sinceira, Brasfemes, 3020-577 Coimbra