Viña del Mar is in Central Chile and is a beach resort town close to Santiago de Chile. It's the most important beach in the country. It plays host to a famous music festival every year in late-February.
Beyond frequent coach bus service between Santiago and Viña. Numerous operators, abundant seating, about a 90-minute ride (but considerably longer if there's traffic) for approximately CLP$5000 one way. The buses depart from Santiago at Pajaritos Station (Line 1 of Metro Station) or Universidad de Santiago Station, is recommendable to do it from Pajaritos Station if you want to avoid the stop over from Universidad de Santiago and the ride within the City. The 2 main lines that travel to Viña del Mar are Turbus and Pullman Bus. The bus will drop you at Rodoviario Viña del Mar (Viña del Mar Bus Station), which is 3 blocks east of DownTown (Valparaiso Street 1055). Taxis are available at this point, but if you want to save some money, walk east to Plaza de Viña, and ask for transportation to your destination.