Family vacations make wonderful memories, but they're also challenging. "If the kids are happy, the parents are, too," or so the saying goes. If you're on the road with the family this summer, check out these suggestions for family fun.

SANTA CRUZ BOARDWALK

A special link between Honolulu and Santa Cruz, Calif., was celebrated last month in Hawaiian style. At Santa Cruz Lighthouse Point, a brass plaque designed by Kristin Zambucka was unveiled paying tribute to Jonah Kuhio Kalanianaole, David Kawananakoa and Edward Keliiahonui, who introduced surfing to the Mainland riding redwood surfboards at the mouth of the San Lorenzo River in 1885.

Santa Cruz summers offer more than great surf. Within walking distance of the Lighthouse, which has its own surfing museum, the Santa Cruz Beach Boardwalk remains one of the best old-fashioned amusement parks in the country: a half-mile strip of thrill rides, shops and restaurants right next to a beautiful beach.

Best thing: Of the 34 rides, two are national historic landmarks: the Looff Carousel, built in 1912, and the Giant Dipper, built in 1924, welcome the kid in all of us. And there are plenty small-scale rides for the under-36-inches crowd.

Simple seaside fun is daily from May 22 through Labor Day weekend. Admission to the boardwalk is free; tickets for rides are separate. www.beachboardwalk.com. All ages.

MONTEREY BAY AQUARIUM

Imagine gaining 800 pounds in 14 months — all on a diet of jellyfish. At the Monterey Bay Aquarium, the giant ocean sunfish, a bizarre creature whose body weight can reach 5,000 pounds, is just one of the watery wonders on view. Monterey Bay's immense glass tanks nurture more than 35,000 animals and plants.

The Outer Bay tank, one of the world's biggest windows on ocean life, lets you eyeball yellowfin tuna, green sea turtles, barracuda, sharks, giant ocean sunfish and dozens of other species. In another tank, jellies, rays and huge schools of mackerel swim between three-story-high forests of kelp.

The aquarium sits above the border of the Monterey Subterranean Canyon — a marine abyss wider and deeper than the Grand Canyon — and in "Mysteries of the Deep," a short presentation screened several times daily, visitors can see the canyon's deep-sea creatures captured on film from robot submersibles.

"Hot Pink Flamingos: Stories of Hope in a Changing Sea," the aquarium's new summer exhibition, addresses climate change in the oceans, and there are daily outdoor encounters with albatross and friendly sea otters.

Standout feature: The Splash Zone, a 7,000-foot area with 45 interactive features for children under 9 including a 40-foot-long touch pool and a kelp forest tunnel.

Monterey Bay Aquarium, 886 Cannery Row, Monterey, Calif. 800-222-2558, www.mbayaq.org. All ages.

HOOVER DAM

Even for supercool teens, the Hoover Dam, near Las Vegas, is a showstopper. This "concrete colossus" stands 726 feet from bedrock to the roadway that crosses it. The towers on top add another 40 feet.

In the 1930s, President Herbert Hoover, himself a civil engineer, pushed forward the project to block the Colorado River at Boulder Canyon to generate enough electricity and means of irrigation for Arizona and California.

The project stats are mind-boggling. According to the official tour site, the dam contains enough concrete to pave a two-lane highway from San Francisco to New York City (and the official word is that no one is buried in the wall). Also impressive is its completion in five years.

Most memorable: Taking the big elevators 500 feet down into the wall of Black Canyon, walk through a 250-foot-long tunnel drilled out of rock, to view the massive generators.

The Hoover Dam sits on the border of Arizona and Nevada, an easy 30-mile drive from Las Vegas. For tours from Las Vegas: www.lasvegastourism.com/hoover_dam.htm. More awesome Hoover Dam stats are at www.usbr.gov/lc/hooverdam/faqs/damfaqs.html. Ages 8 and up.

EXPLORATORIUM

Celebrating its 40th year, San Francisco's epicenter of hands-on cool science stuff challenges young (and not-so-young) minds in a relentless array of interactive exhibits all housed in an old airplane hangar. Where else could you find a grand piano suspended from the ceiling? Or find a wave organ — a slab of concrete embedded with listening tubes that lead underwater to record ocean currents as a harmony of gurgles and sloshing sounds.

This summer, in the new Science of Baseball exhibit, young fans can explore why a curveball curves, what they put in the middle of a baseball, why players learn to run on the balls of their feet, and why the singer needs to wear earplugs to get through the national anthem.

And if you're not a baseball fan there are heaps of other things to do, plus short talks for the biggest kids in the family, often the ones who drive the car.

10 a.m. to 5 p.m. daily, closed Mondays, Palace of Fine Arts. $15, adults; $12, students, seniors and ages 13-17. www.exploratorium.edu. All ages.

SAN DIEGO ZOO

The San Diego Zoo shelters more than 4,000 animals including its famous panda family, and the range is extensive: kiwis from New Zealand, lowland gorillas from Africa, giant tortoises from the Galapagos, polar bears, Mongolian horses and an immense aviary of birds. The zoo offers a guided bus tour of the grounds, or you can hop on the Skyfari aerial tram for a bird's-eye view of the 100-acre facility. A two-in-one package includes the San Diego Wild Animal Park, 34 miles north of San Diego where ostriches, giraffes, antelopes and zebras roam freely in vast enclosures.

What's on this summer: For the zoo's extensive calendar of summer events: www.sandiegozoo.org/calendar/calendar_highlights.html

ROCKY MOUNTAIN NATIONAL PARK

For a road trip with eye-popping scenery, it's hard to beat Colorado's Rocky Mountain National Park. Seventeen peaks above 13,000 feet, dozens of trails through forests of ponderosa pines, juniper and blue spruce, wandering elk, bighorn sheep and in summer months, wide meadows of wild flowers.

Trail Ridge Road is the park's primary east-west roadway and one of America's great alpine highways. It is the highest continuous motorway in the United States, with more than eight miles above 11,000 feet. The 48-mile scenic drive from Estes Park to Grand Lake takes about three hours. There are visitor centers along the way for rest stops.

Take a break: Rock Cut parking area (elevation: 12,000 feet) about halfway along the scenic drive has spectacular views of the Continental Divide. And you can stretch your legs on the half-mile nature walk. www.nps.gov/romo.

GRIFFITH PARK

High above Los Angeles, Griffith Observatory's major renovation was completed in 2006. The large central dome houses a 300-seat planetarium with what is described as the most advanced star projector in the world. Three different shows are offered each day, including a very cool laser show.

In the Hall of Science, exhibitions on galaxies, meteorites and astronomical fare share space with a Foucault pendulum that demonstrates the Earth's rotation.

Two domes flank the building: the west dome contains a solar telescope trained on the sun for daytime visitors; in the east dome, a 12-inch refracting telescope is available for evening visitors to gaze at the moon and planets. And for evening visitors, Griffith Park's panoramic view across the city is spectacular.

Noon to 10 p.m. Tuesdays-Fridays; 10 a.m. to 10 p.m. Saturdays and Sundays. Closed Mondays. 2800 East Observatory Road, Los Angeles. www.griffithobservatory.org.

CARLSBAD CAVERNS

Carlsbad Caverns National Park in southeast New Mexico is one of the world's largest and most complex cave systems. Some 100 known caves of ghostly limestone contain spectacular stalagmite and stalactite formations in every shape imaginable: frozen waterfalls, fairytale turrets and runways to nowhere. This vast subterranean network 800 feet below ground is a constant cool 55 degrees Fahrenheit.

Visitors can take the elevator from the visitor center down 750 feet to the Big Room, an immense rock chamber that covers 14 acres. Or take the one-mile walkway from the natural entrance down through a series of rooms to arrive at the Big Room. From there an optional self-guided tour is available, with rangers at interesting points along the way.

Don't miss: The massive bat flight at sunset, when thousands of Mexican free-tailed bats launch from the cave entrance out over the desert for dinner (May through October). 8 a.m. to 7 p.m. daily. Carlsbad Caverns National Park is about 150 miles east of El Paso. $6 (ages 15 and under are free). Ages 6 and up. www.nps.gov/cave.