Take the L5 bus at Praza de Galicia or Praza Roxa, for instance, inbound A Rocha and alight at the last stop: A Rocha Vella.
From there, come back to the roundabout located just before the bus-stop and follow Serafín Zas Street. A few meters after the roundabout, take Do Piñeiro Street to get to the castle.
The fortress is located near to the Viaducto da Rocha, the road bridge over the river Sar. To get to the castle by car, you should leave Santiago towards O Milladoiro, Pontevedra or Vigo (N550). Passing the road bridge over the Sar, you may take the road to A Rocha Vella just at the end of it, on your right.
Once you take the detour downhill, go to the first exit (Churruchao Street) to a new, smaller roundabout. Again take the first exit on your right (Serafín Zas Street) and then go straight to Do Piñeiro Street to get to the castle.
How to get to the first bridge
From Santiago, you can take Av. Xosé Filgueira Valverde, Av Antonio or Rúa da Volta do Castro, all of them meeting together at the roundabout Volta do Castro. From there, you may follow the road in direction to Pontevedra for 300 yds, passing that viaduct.
You can also get to that roundabout from the N-550 (traveling North), the motorway AP-9 or the also motorway AG-56.
You can walk to the castle following the itinerary of the Portuguese Way through the town of A Rocha Vella.
From there, continue along Rúa Serafín Zas (linking A Rocha Vella and A Rocha Nova) and then follow Rúa do Piñeiro on your left to get to the fortress.