Viña's bar and cafe scene is relaxed and unhurried — this is a resort city, and people come here to decompress. The centre has a handful of good cafes for morning coffee and afternoon pasteles, and the bar scene picks up in the evenings along the streets near the Casino and around Cerro Castillo. Pisco sour is the default order and comes in many variations; ask for a good one and you'll get a debate about the correct recipe.
For a quieter drink, the cafes lining the Marga Marga estuary and the streets around Quinta Vergara fill pleasantly in the late afternoon. The casino bar is worth a visit for the atmosphere alone, even if you're not gambling.