From Stellwagen Bank to Gray's Reef, from the Channel Islands to the Florida Keys, from tiny Fagatele Bay sanctuary (one-quarter square mile) to the mammoth Monterey Bay sanctuary (5,300 square miles), America's 13 national marine sanctuaries are a fun paradise where you might kayak through dripping sea caves or shadowy mangroves, surf empty waves, dive a wreck hung with shimmering barracuda, or gulp a lungful of air and fin down through the water column to hang motionless in the blue, listening to the long wails from singing humpback whales. Should you opt to stay dry, the magic is undiminished. There's interactive video­ that brings the kelp forest to you; untrammeled tide pools in which to poke about; stellar fishing and birding (several sanctuaries are home to birds found nowhere else); and wildlife-watching trips where any surprise might rise from the ocean - rare northern right whales, frolicking humpbacks, or perhaps an ocean churned to a white-capped frenzy by the explosive play of 1,000 common dolphins.

First, though, you must realize that these marine sanctuaries exist. The United States' first sanctuary, the Monitor National Marine Sanctuary off Cape Hatteras, North Carolina (monitor.noaa.gov, 757-599-3122) - encompassing the waters surrounding the wreck of the famous ironclad Civil War vessel USS Monitor - was founded in 1975. The process has continued quietly.

Countless Americans have stood before the whump and gush of Old Faithful. But only a handful of Americans can find the Flower Garden Banks sanctuary - home to the country's northernmost reef - on a map.

The Channel Islands National Marine Sanctuary (channelislands.noaa.gov, 805-966-7107), its spread of waters wrapping five islands and extending six miles out to sea, was formed in 1980. Yet even among Southern Californians, the sanctuary remains largely unknown and, in governmentspeak (the sanctuaries fall under the auspices of the National Oceanic and Atmospheric Administration), sorely undervisited - almost to the point that sanctuary personnel find themselves in the odd position of both guardian and carnival barker.

"The term sanctuary may scare some people off," muses Chris Mobley, manager of the Channel Islands National Marine Sanctuary. "Certainly the primary responsibility we have is to protect the waters. But we allow plenty of opportunities for people to do things out there."

Mobley pauses.

"The door is open, with a big welcome sign on it," he says.

Happily, ignorance and undervisitation are synonyms for the solitude that facilitates wilderness magic. I live in Ventura, California. Sanctuary waters rest just five miles off my home beaches. I have snorkeled with sea lions off Santa Barbara Island, kayaked into the sea caves of Santa Cruz, dived the kelp forests off many of the islands, and watched pods of gray whales send misty contrails into the air. And always there hangs the specter of the unexpected. Anchored off Anacapa Island one afternoon, eating lunch by myself on the bow of a friend's boat, I lifted my peanut-butter sandwich to my mouth. As my eyes met the horizon, an orca leaped clear of the water.

Sanctuary manager Mobley has his memories, too. Aboard the 62-foot NOAA vessel Shearwater, Mobley once found himself surrounded by the grandest creatures on earth.

"Twelve blue whales," he says. "They were feeding, taking dives, showing their tails. Each one of those whales was twice as large as our boat. It was unbelievable."