Ribeiro's biggest winery, selling 5 million bottles a year, Costeira offers 45-minute visits to its production facilities 3km northeast of Ribadavia, with tasting of one wine. In theory you don't need to book (except for the 5pm visit). However it's still advisable to check with the tourist office, or phone the winery in advance, to confirm tours are happening, especially if you want a tour in English.
Also on offer are longer visits including vineyards (for which you need your own vehicle) and tasting of two wines (€5, 90 minutes) or four wines (€10, two hours). For these, reserve at least 24 hours ahead.