In February 2007 I took my rental car and drove on some of Puerto Rico's twisting mountain roads. There are some areas along the Luis Muñoz Marín panoramic route that crosses the island from east to west where you can see both the Atlantic and Caribbean coasts, as well as some of the island's tallest mountain peaks.
This view faces the city of Ponce to the south and the Caribbean Sea in the distance. I met a Puerto Rican family who was taking in the same views, and they told me that relatively few Puerto Ricans visit this area compared to the populated coast.
See my webpage on Puerto Rico at http://www.latinandcaribbeantravel.com/puertorico.html