Visiting wineries in Galicia

My wife and I will have a day in Galicia next month and would like to visit a winery or two (or three). Can anyone give any guidance or suggestions? We’ll probably go to Martin Codax because that’s the one with which I’m most familiar but am interested in discovering something new. It appears most are open only by appointment. Does anyone know if there are any that have tasting rooms you can visit without appointment? Thanks.