Watch toothy sharks zigzag through the water inches from your sleeping bag at SeaWorld Adventure Park (1-800-327-2424; www.seaworld.com) in Orlando; bed down under the formidable frame of a Tyrannosaurus rex at the Field Museum (312-922-9410; www.fieldmuseum.org) in Chicago; or count stars as you fall asleep under the recreated heavens of the multi-million-dollar planetarium at the Saint Louis Science Center (1-800-456-SLSC; www.slsc.org). These are just a few of the ultimate insider slumber parties available at museums, science centers, and zoos across the United States.

The unique experience of staying overnight at a museum or zoo works well for busy parents and children, plus those on a budget, as it offers an opportunity for children to take imaginative adventures close to home. It also allows vacationing families to dodge the tiresome crowds at some of the country's busiest theme parks. The overnights generally cost from $45 to $135 per person, though you can spend more for a few extra amenities and luxe trimmings. Most facilities' overnights cater to scout and school groups; therefore, private sleepovers should be booked months in advance. And remember, if parents aren't available, family sleepovers always welcome grandparents and grandkids with open arms.

Although mealtime consists of pizza or sandwiches, and bedtime finds you flopped on the floor in your own sleeping bag, the programs pack enough excitement to make you forget about the not-exactly-luxurious accommodations. As part of the immersive learning experience, the overnights have guides who lead you and your kids behind-the-scenes for activities that day-visitors can only dream about—think flashlight tours of the Egyptian mummies at the Field Museum or popsicle-making for the polar bears at SeaWorld.

Slumber parties at zoos and wildlife theme parks feature (what else?) animal encounters. On a twilight walk at the Miami Metrozoo (305-251-0400; www.miamimetrozoo.com), view lions, tigers, and other nocturnal critters who morph from daytime dozers into keen-eyed prowlers as the sun sets. The overnight Zoo-Inn requires you have 15 to 30 people in your group, so think of this as a blockbuster option for a big family reunion or birthday bash. At Zoo-Inns, available year-round, the education center classroom provides the slumber area. For those who like the activities but not the bedding arrangements, try Wild Night, an after-hours, behind-the-scenes tour.