PR-191 follows a north–south path through El Yunque National Forest and the Sierra de Luquillo and is divided into two non-contiguous sections.

[4] The highway begins at PR-955 in the community of Palmer in the municipality of Río Grande.

From there, it climbs into El Yunque National Forest 4 km from its beginning.

The road is closed to public traffic through part of the forest starting at a point 13.1 km from the beginning in Palmer and immediately past PR-191's second junction with PR-9938 (which is signed "Ramal 938") and just before a junction with Forest Route 10 and near the Mount Britton and El Yunque Peak trailhead.

The highway continues south out of El Yunque National Forest passing the village of Florida and ending again at PR-31, near Río Blanco in the municipality of Naguabo.