When the tides get low, new worlds emerge along coastal destinations, and seaside explorations are worth their weight in surprises. Here's the lowdown on three part-time playgrounds.  

The great thing about hidden beaches is also the trouble with hidden beaches—they're hard to find! So remember these five words: Hole in the Wall Beach. About 10 miles north of Santa Cruz, this golden stretch of sand, backed by 30-foot cliffs, has several small enclaves for some R&R. Getting there requires a scramble down a well-worn path to Panther Beach. Then look south toward the giant (12 feet across!) hole in the rock wall, and stroll through this natural tunnel to the beach. As with most hidden beaches, the area is sometimes inhabited by the clothing-optional crowd. And it's accessible only at low tide, so when you see the ocean rising, head back to the hole.

Low tides: March 15, 12:58 p.m. (-.5); March 16, 1:56 p.m. (-.6). For information on more upcoming low tides, click here. Directions: Just south of Davenport on Highway 1, start watching the mile marker signs. Between mile markers 26.86 and 26.40, about a half-mile south of Fambrini's Farm Fresh Produce, there's a dirt pullout on the west side of the highway. Coming from the north, take a sharp right turn at the pullout. Park—leave no valuables in the car—cross the railroad tracks, and scramble down the rocks to the beach. Swimming isn't advised because of strong riptides. Dog-friendly!

Fitzgerald Marine Reserve, just north of Half Moon Bay, is a popular low-tide destination. The receding sea reveals rocky reefs the length of a football field, offering a beachside glimpse into an underwater world. Residents include a rich variety of marine life such as sea stars, crabs, sponges, sea anemones, and mollusks. Kids abound, too, getting up close and (sometimes a little too) personal with sea creatures; touching is encouraged, but don't let the crabs pinch! Spring is one of the best times to visit: the resident harbor seals, of which there are more than 100, are pupping. Approaching these newborns is prohibited, but it's amusing to watch them from a distance. Even Gatsby would be rapt…

TIP: Keep an eye out for informative volunteers wearing green shirts; they're part of the Friends of the Fitzgerald Marine Reserve and have been active in maintaining and educating people about this strip of coast for over 20 years.

Low tides: March 15, 12:53 p.m. (-.2), March 16, 1:58 p.m. (-.3). For information on more upcoming low tides, click here. For more information on Fitzgerald, click here. Dogs and groups of 10 or more are not allowed.

To walk along Marin's Muir Beach at low tide is to visit a virtual sea star sanctuary. Stroll north, cross the gently flowing Redwood Creek (it's shallowest and easiest to cross closest to the ocean), and start rock-hopping, betting on who can spot the most colorful treasures. Some rocks, like those nearest to the ocean, burst with dozens of sea stars. Watch your step and navigate around the hundreds of sea anemones that reside here as well. After getting starry eyed over sea stars, head just past the rocks for another low-tide-only locale: a sheltered sandy cove, perfect for kicking back and watching the waves. San Francisco's Sutro Tower is visible in the distance—but city life feels far away.

Low tides: March 15, 1:33 p.m. (-.2), March 16, 2:38 p.m. (-.3). The best time to explore is a negative low tide. For information on more upcoming low tides, click here. As with every low-tide exploration, keep an eye toward the ocean for rogue waves. Muir Beach closes at sunset. For directions and more information on Muir Beach, click here. Dog-friendly!

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