I second Valparaíso and Viña, was there in December 2017 and loved it. Valparaíso is a UNESCO World Heritage site. Lots of history—take advantage of the free tours (Tours 4 Tips)—they are terrific (ended up taking 1 in Santiago, 2 in Valparaíso and 1 in Viña Del Mar). Visit Pablo Neruda’s house, walk the beach in Viña and Reñaca, hike the hills of Valparaíso. The food is outstanding and the wine region of Casa Blanca is close enough for an easy day trip. If you find extra time on your trip, go to Pisco Elqui. It’s on the Ruta de las Estrellas, star gazing is outstanding. Plus it’s the home of many Pisco distilleries (you will have many Pisco Sours in Chile). Pisco Elqui is very similar in climate, geography as Arizona. Spent two nights there and it was a highlight (flew from Santiago to La Serena (1 hour) and then a bus (3? hours) to Pisco).