Drive to the very top of road #191 on the north side, through Palmer. You will find a sign with an arrow pointing to the Mt. Britton parking. The trail begins there.
The Mt. Britton lookout tower, on a small peak, is a great hike. 45 minutes up, less down. 3,088 ft. high. It is a wonderful overlook of the El Yunque Rain Forest, on a clear day you can see forever! On a cloudy day, with a little wind, the clouds are swirling around you. Great experience, well worth the hike up. There are 3 covered rest stations on the way up.
You walk through the Sierra Palm forest as you climb. The path itself is paved, perhaps narrow but well maintained. If you wished to continue up to the top of El Yunque the path continues from here ( about another hour up).