We'd never given San Juan, Puerto Rico, a second thought as a ''bring the kids'' vacation destination. To us, it was just a portal to more exotic island destinations.

We adults had done a brief tour of Old San Juan on a layover, and enjoyed the cobblestone streets, candy-colored facades and criolla cooking of this World Heritage city, but kid-appeal? Nah! We've been around the block enough times to know that a centuries-old capital doesn't rate high on the list of must-sees for our adventure-loving bunch. We could just imagine: ``Mo-omm! Do we really have to see El Morro? We already saw San Cristobal!''

But, thanks to an airline snafu that resulted in some free tickets, San Juan started looking pretty good. (It was the only place we could afford to go on the cheapie tickets.) Surely we could find some outdoor action that would sell our teens on the charms of this destination.

Did we ever. We hedged our bets (and garnered some Cool Mom points) by staying at a hotel with the liveliest pool scene ever, the El San Juan, and rented a car so that we could get out and explore the hilly areas beyond the city. Here's what we discovered, from mild to wild.

NATURE'S HOT TUB

Head 40 miles east, and the hillsides turn deep green, the outlet malls disappear and you arrive at 28,000-acre El Yunque, the Caribbean National Rainforest -- the only tropical rainforest in the United States.

Wild animals are few here, unless you count the mongoose and the (rare and endangered) Puerto Rican parrot, but exotic blooms are abundant and gorgeous. Torch ginger, slipper hibiscus, flaming red ginger and ''lobster claws'' grow everywhere, sharing the soil with bananas, breadfruit and mangoes.

The day was hot and humid, but the rainforest was a cool refuge. We meandered along La Mina Trail, accompanied by the sound of running water. With four rivers flowing through the park, there are tumbling cascades at nearly every turn.

Halfway through the hike, we reached Cascada La Mina, a splendidly bushy waterfall, with pools at its base. Great for splashing around in, as a dozen visitors had already discovered.

''This is like a water park, without the cement,'' 15-year-old Jarrett remarked, pulling his T-shirt over his head and boulder-hopping toward the waterfall. The rest of us quickly followed suit. For our city kids, a dip into Mother Nature's hot tub was an unexpected treat.

Back on the trail, we Moms reveled in the earthy green scent and damp beauty of the rainforest. Meanwhile, Jarrett and Connor, 17, were contemplating Tarzan-like moves on the huge, ropy vines that dangled over the trail. (''Just. Please. Don't!'' we said, in that no-nonsense Mom-speak that still works, in public anyway, on our teenagers.)

The kids were eager to get back to the hotel and catch dinner at the El San Juan hotel's Tex-Mex restaurant (translate: connect with some kids they'd met at the pool and ride the mechanical bull).

BIOLUMINESCENT BAY

This one takes some doing, but it is so worth it! In Fajardo, about an hour's drive east of San Juan, we caught the ferry ($2) to Vieques, a lovely little island about seven miles off the coast. A quick taxi ride got us to the beach town of Esperanza, where Blue Caribe Kayaks would take us out after dark to commune with the dino-flagellates. These microscopic organisms live in the waters of Mosquito Bay and emit light when they get riled up.