About 45 kilometers north of Santiago [1], in the Andean foothills but close enough for a day trip, Termas de Colina is a woodsy hot-springs resort in a scenic dead-end canyon just outside the town of Colina. Its mineral waters reach a natural temperature of 31°C, warm enough for a comfortable soak but not exactly hot-tub intensity.
Owned by the army, Hotel Termas de Colina (Camino Las Termas s/n, tel. 02/8440990, termasdecolina [at] yahoo [dot] es, US$32/52 s/d with continental breakfast) features spacious rooms with balcony views of the surrounding sierra; its restaurant also serves lunch and dinner. Day-trippers can use the Olympic-size pool (US$9 pp), thermal baths (US$6 pp), sauna (US$11 pp), or Jacuzzi (US$11 pp).
Buses Colina (Av. La Paz 350, Independencia, tel. 02/7374572) goes every 10 minutes or so to the town of Colina (US$1.25, one hour), but it’s necessary to hire a taxi for the last several kilometers to the Termas.
Links:
[1] http://www.moon.com/destinations/chile/santiago-and-vicinity