The whole coastline of the rias baixas is so dotted with fine beaches that it would be pointless to get very specific. They are nearly all sign-posted off the main road so a policy of experimentation is something to consider, if you feel like venturing away from the resorts of Sanxenxo and Portonovo, etc. Easily the most impressive (i. e. biggest) beach is that of La Lanzada, near O Grove. But, for example, if you drive towards San Vincente from here (or, indeed, in the opposite direction) you will find beaches galore. In early July there are not many people on these. In June and September, hardly anyone. Another excellent option is to drive from Pontevedra to Marín and try the beaches just past the latter. Or further long the edge of the ria towards Cangas and round the headland. Note that some of these beaches are for nudists.
One thing to bear in mind is that the locals – and Spanish tourists – are creatures of habit. They all go for their main meal of the day from 1 to 3pm and then possibly take a rest, or even sleep. They then return to the beach in the early evening. So, between 1 and 5, say, you could well find the beaches much emptier than at other times. On the hand, you will naturally find the roads fuller during the periods of mass transit to and from the beaches.
If you are looking to get the bus out of Pontevedra to the beaches along the coast towards and beyond Sanxenxo, it leaves from Praza Galicia. The timetable is at the back of the local newspapers.
One beach I have decided is worth citing is that of Las Dunas de Corrubedo. This is a gorgeously long stretch of sand and turquoise sea, backed by lofty dunes. You will find it near Santa Uxía (also called Ribeira), at the end of the Via Rapida from Padrón (VRG-11), about 60km from Pontevedra. The more of you who go there, the less chance of overcrowding on my own favourite beach.
A final comment on beaches – the water may look wonderful but, even in mid-summer, one is risking one’s manhood to stay in it too long. Or, indeed, to enter it. It never gets more than just-about-tolerably-warm. To be honest, that’s an exaggeration; in my experience, it rarely gets above bloody freezing. That said, friends of mine insist that there are beaches where the water is appreciably warmer than elsewhere. One of these - Montalvo - is on the coast road from Sanxenxo to O Grove. This, too, is a nudist beach. For one reason and another, I have not checked out the claim that the water is warmer there. Other things clearly are.