I've been lucky enough to spend a bit of time in O Grove over the past couple of years since making a few friends there. It's a lovely town and peninsula with many beaches on all sides. Lanzada, San Vicente, Area da Cruz, and Mexioeira are the largest, but there are many other small delightful beaches to discover (Area Grande, Playitaa, do Con, de Canelas, Abelleira, Pedras Negras (the best spot for sunsets!), Canina, and de Rons to not even name them all). Despite having so many beaches, and it's not quite the same (sometimes a bit wild) party vibe that you find in Sanxenxo. As scruffy mentions, Isla Toxa is connected by bridge to O Grove, which is where the shell covered chapel dedicated to la Virgen del Carmen is located. Isla Toxa is also home to many fine upmarket hotels/resorts, many of which feature nice spas ('balnearios' in Spanish). In O Grove itself, there are many more affordable options available.
Not only are clams harvested there (the "marisqueiras" with the rakes collecting the clams are actually all women), but you can also see the floating wooden rafts a bit offshore where mussels are farmed. There are many other kinds of shellfish to be found up and down the coast in Galicia. One of the best and most well regarded seafood restaurants in all of Spain is located in O Grove,
d'Berto Restaurante, located just 500m before you get to the bridge to Isla Toxa. I wrote a couple of blog posts about our visits to d'Berto
here. I still have lots of blogging to do about other great places in O Grove, such as Pan de Millo, Culler de Pau, and Taberna Meloxeira.
If you find yourself in the area during the first two weeks of October, O Grove hosts a 10 day annual
Festa do Mariscos (Shellfish Festival), for 52 years running now. We went last year and it was great fun, with lots of cultural activities (traditional dance and music, expositions) and of course endless amounts of wonderful seafood!
O Grove is also a nice jumping off point for exploring the Rias Baixas wine region. There's a bit more information about the neighboring wine regions at the bottom of the d'Berto post linked above. There's an aquarium and fishing museum with a neat sculpture park near a lighthouse in between the two that makes for a lovely afternoon visit. The bus station is located in the main port area (by the city hall - which is also where the Shellfish Festival takes place), but I don't know about the actual options, we have always arrived by car.