El Yunque National Forest in Puerto Rico is one of the island's must go to attractions. Covering over 28,000 acres, El Yunque is a lush rainforest with peaks soaring over 3,000 feet (1000 meters), cascades, streams, views, and a diverse flora. The park is a short drive (45 minute drive) from San Juan and tickets are less than $10 per car.
There are three main trails, ranging in difficulty, from 0.8 miles to 2.4 miles. Although typically cooler than the island's coast, you should make sure to bring water on hotter days, as there is no potable water (do not drink the water from the streams, as it could could contain Giardia which can make you sick).
It rains over 20 feet (6 meters) every year in El Yunque. You can expect sporadic showers on any given day, so the trails can be slippery.
There are three observation towers:
Yokahu Tower can be accessed by car and it's the lowest of the three.
Mt. Britton Tower can be accessed by hiking the 0.8 mile (1.3 km) Mt. Britton Trail
El Yunque Peak Tower can be accessed by hiking the 2.4 mile (3.9km) El Yunque trail
The Tabonuco tree is one of the endemic species that can be appreciated in the Big Tree Trail. The trail is 0.9 miles (1.4 km) long.
For more info visit the USDA site: https://www.fs.usda.gov/main/elyunque/home