To visit the Southwest [1], you could cover some major attractions in just a few days. Perhaps take a three-day weekend away from the city to make your way over the Península de Pedernales [2] or scope out a driving loop around Lago Enriquillo [3]. Whichever direction, inland or coastal, the best town to look to for a home base is Barahona [4]. It offers the best accommodations options and has some semblance of a nightlife, albeit small.
If you plan a day at the beach, make it Bahía de las Águilas [5] and save a day for it. You’ll want to get there midmorning to have a day at the beach, so you’ll have to spend your morning gathering provisions and securing the boat ride. The same is true for a loop around Lago Enriquillo [3], with the tour of the lake being only a couple of hours long.
Links:
[1] http://www.moon.com/destinations/dominican-republic/the-southwest
[2] http://www.moon.com/destinations/dominican-republic/the-southwest/peninsula-de-pedernales
[3] http://www.moon.com/destinations/dominican-republic/the-southwest/peninsula-de-pedernales/lago-enriquillo-loop-road/parque-nacional-isla-cabritos
[4] http://www.moon.com/destinations/dominican-republic/the-southwest/peninsula-de-pedernales/barahona
[5] http://www.moon.com/destinations/dominican-republic/the-southwest/peninsula-de-pedernales/bahia-de-las-aguilas