There is a Roman Villa (what remains of one) to the north of town, if you are staying in town it makes for a good afternoon trip of about 800m each way.
There are no services along the next 11km to Conímbriga. Stock up in Rabaçal, the night before if you have to.
Keep on out of town along the road and turn right where indicated in the direction of the Castelo de Germanelo. A turn to the left appears 900m down this road. Turn there and follow a well-marked set of trails all the way to Zambujal.