Marathon, Florida

Why: Marathon is a quieter alternative to Key West and only a two-hour drive from Miami.

What to Do: Drive north and south on the road that links the Keys, gazing at less developed islands. Stop for breakfast at Leigh Ann's coffee shop on your way to the Dolphin Research Center, on Grassy Key, 10 minutes from Marathon.

Where to Stay: Tranquility Bay has two- and three-bedroom beach houses (from $1,794 a week, www.tranquilitybay.com).

Orcas Island, Washington

Why: Orcas, the largest of the San Juan Islands, has two big sights: Mount Constitution, the highest point on the islands, and whales. "During the summer, you see whales every day. It's a thrill," says Jeremy Trumble, co-owner of the Inn on Orcas Island. Bonus: The San Juan Islands don't see much of the rain that hits the mainland and get half as much precipitation as Seattle.

What to Do: Visit the art gallery at Crow Valley Pottery, in the village of Eastsound. And sample organic food at Christina's Food & Wine restaurant. "If Christina can get her ingredients from the island, she does," says Trumble.

Where to Stay: The Inn on Orcas Island (doubles from $145, www.theinnonorcasisland.com).

Sanibel Island, Florida

Why: The beaches of the Gulf Coast have some of the most beautiful white sand in the world.

What to Do: Get up early and look for shells on the beach. Because of the beach's east-west orientation, shells wash up by the bucketful. Keep a lookout for junonias, rare conical shells with brown spots. "They are very prized. When someone finds one, they get their picture in the paper," says David Meardon, a photographer who has lived on Sanibel for 25 years. Hungry? "The Lazy Flamingo has the best mesquite grilled–grouper sandwich you can find," says Meardon.

Where to Stay: The Sundial Beach & Golf Resort (doubles from $379, www.sundialresort.com) offers kids' activities and games.