El Yunque, the only rain forest in the U.S. national forest system, was, we'd been told, another world. In Puerto Rico, that's not saying a whole lot. On an island that is at once starkly urban and lushly tropical, where in three quick miles you can drive away from an empty white beach, watch a swarm of bulletproof-vested police close in on a drug thug at a highway strip mall, and end up at a family festival in the center of a rural village--here, every turn seems to reveal another world.

So when we arrived at the visitor center at the gateway to the Caribbean National Forest, there was little shock in seeing those familiar green uniforms of the U.S. Forest Service rangers. The men in green switched easily from English to Spanish and back again, answering questions about the Puerto Rican parrot (no, you're not likely to see one; there are probably fewer than 100 still alive), the damage from Hurricane Georges (extensive to roads and buildings, but once you're past the visitors center, hard to notice amid the dense foliage) and the best view (just head up the mountain--the vistas in all directions are breathtaking.)

The center, which opened in 1996, has plenty of kid-friendly exhibits about the forest and what's in it, as well as a film, narrated by actor Jimmy Smits, that tells the history of El Yunque and the Taino Indians, who gave us, among other things, the words "hammock," "canoe" and "hurricane."

The words "rain forest" alone had worked the kids--Julia, 8, and Aaron, 3--into a frenzy of anticipation. Never underestimate the ability of children to create concrete visions of abstract concepts. Julia had her heart set on seeing a spring. "The kind spring water comes from," she said. Aaron, of course, wanted a forest--with rain in it. As for the grownups, we had scarcely any sense of what to expect. "A jungle," I told the kids. "Like Tarzan."

Which naturally provoked about an hour of questions about what "jungle" and "Tarzan" meant.

We drove up Highway 191 through the Luquillo Mountains planning a relatively easy hike, one that might conceivably end with the four of us on our own legs and no one on anyone's shoulders. The road is narrow and winding, washed out in numerous places by Georges, which hit Puerto Rico with savage force last year. Each turn reveals another side of the island's striking diversity--a picture-window seascape, waterfalls ranging in intensity from bathroom showers to raging rivers, mountains lost in the clouds, hillsides of stunted vegetation (the so-called elfin forest), a tiny roadside stand selling coco frio (chilled coconuts with their tops chopped off and a straw stuck in to reach the milk).

Even during spring break, we seemed to have the forest to ourselves, though we did run across families, groups of college students and serious hikers on the trails. El Yunque, which consists of 28,000 acres of eastern Puerto Rico first salvaged from development by King Alfonso XII of Spain in 1876, derives its name from a Taino Indian term for the good god who protected them from all that was evil. Today, El Yunque serves a similar purpose for Puerto Ricans, who depend on it for about a fifth of their water, three-quarters of their remaining virgin forest and a spectacular array of plant and animal life--including the coqui, the brown tree frog, named for its songlike call, that has become the symbol of the island.

We chose a trail that wended its way to La Mina Falls. It was a concrete and stone path, one of many aspects of the forest that had a 1930s Civilian Conservation Corps look to it--sturdy, dated, an example of the glory days of federal projects. More ambitious hikers follow the El Yunque Trail, which leads to the top of El Yunque mountain (elevation 3,500 feet), where a Civilian Conservation Corps observation deck from the '30s still stands.

We were perhaps 20 minutes into our downhill leg when the first drops fell--entirely predictable for a forest that gets 200 inches of rainfall a year, but we were, of course, utterly unprepared.

Aaron was thrilled. Now he had both forest and rain.

But then came the downpour, a classic tropical drenching. The stream swept over the path, and the complaints shifted from "I'm sweating" to "I'm freezing" faster than the water could fill our sneakers.

"I want to go," Aaron said.

But we found a shelter soon enough and waited out the rain. A couple of cookies revived the crew and before long we were on our way, wet but determined. Julia, intently examining every water source to see if it might be a spring, discovered the Puerto Rican land snail, a triple-swirled brown creature that could be seen traveling at--say it ain't so--a snail's pace. And she found the scarlet petals of the hibiscus, and startlingly tall and strong ferns whose leaves grow at rigid right angles. And, at long last, she found her spring.

Missions accomplished. And no one asked to be carried. Now, that's a different world.

El Yunque, the Caribbean National Forest, lies about 30 miles east of San Juan and just south of Luquillo Beach. There's a $3 fee at the visitors center; for information, call 787-888-1810. For food, there are a couple of small stands about a quarter of the way up the mountain road; both serve a variety of Puerto Rican fried snacks, as well as fruit shakes and coco frios. Camping is permitted in the forest, but there are no facilities. The forest is quite popular among Puerto Ricans as a weekend day trip; tourists will prefer the relative quiet of a weekday visit. For more information, check out www.gorp.com/gorp/resource /US_National_Forest /pr_carib.htm.