The Guanica Lighthouse, or Faro de Guanica, was built in 1893 in the last years of Spanish rule and operated until the 1950s. It sits on a cliff at the western entrance to Guanica Bay with sweeping views across the harbour and the Caribbean. The building itself is now an empty shell — the Coast Guard removed the lens, hurricanes have stripped the roof, and the interior is unsafe to enter.
It's worth the short walk out to the headland for the view alone. The trail passes through dry forest scrub, so wear closed shoes and bring water. Sunset from the lighthouse is one of the best in the area.