In addition to apps that help him get around, like TripAdvisor (TRIP.O) for dining reviews, Google Maps for street directions and Rail Europe for train schedules, Openshaw uses sightseeing apps to avoid the hassle and expense of in-person guides.

Tourism offices, national parks and travel companies have developed hundreds of free travel-related apps to attract gadget-equipped travelers in the last two years. Most apps can be downloaded to the iPhone or Android cell phones, as well as the iPad or iPod, and don't require a constant data connection.

Knowing which to choose is key, since a poor quality product can easily derail a travel experience. "You need to be able to navigate through the app," says Openshaw, who tests each app to get a feel for content, design and ease of use. "I avoid when it just starts at the beginning and leads me by the nose."

Planning a trip? Here are recommendations from travel experts on what to use on your next vacation:

Favorite City App: Hidden London

Cost: Free

Updated in 2012, the app allows travelers to get a deeper look at the delights of this Olympic city. "It really is giving you a list of cool things to do that other guidebooks aren't," says Amanda Scotese, a Chicago-based tour operator and travel writer who visited London this year.

Visitors can use the app, created by London native Martin Smith, to browse under-the-radar landmarks like a quaint café at the Tate Modern and ancient Roman baths. For each of the landmarks, it also lists opening hours, address, website and shows a map location, which requires using the phone's roaming data connection. Scotese compares it to having an in-the-know tour guide.

When looking for other city apps, she skips the ones that simply regurgitate a guidebook, which can mean too much on-the-go reading. "No one wants to be standing on a street corner for 15 minutes reading their phone," says Scotese. The app is available in other cities, including Hidden Rome and Hidden Prague.

Favorite Museum App: American Museum of Natural History Explorer

Cost: Free

New York's American Museum of Natural History started offering its turn-by-turn app two years ago. "It takes you all over the museum, to areas you may never otherwise get to," says Arabella Bowen, executive editorial director at Fodor's Travel in New York.

Users without an iPhone, iPad or iPod can borrow one of the devices from the museum free of charge. The museum also offers one-off apps for temporary exhibits. For instance, its Creatures of Light app accompanies an exhibit about organisms that naturally produce light. The app is set to symphonic music.

Openshaw is partial to the Louvre app. The storied Paris museum allows visitors to download a free app or rent an audio guide on a handheld Nintendo DS to help visitors maneuver the world's largest museum. "Basically, if you have an hour and a half at Louvre, it says: Here's the best way to spend ," he says.

Paying for an in-person Louvre tour can cost a family of four more than $200, Openshaw estimates, versus the 5 euro cost of renting the Nintendo DS.

Favorite Landmark App: Monumental Agra

Cost: $1.99

Touring the Taj Mahal and nearby 17th century ruins in Agra, India can be an overwhelming experience. While the UNESCO World Heritage site draws more than 3 million visitors each year, tour guides are known to be hit or miss. Instead of opting for an in-person guide, Bowen downloaded the Monumental Agra app, created in consultation with academics and historic texts, which let her marvel at the sites at her own pace while getting a dose of Indian history.

The app shows visitors suggested walking tours while highlighting points of interest. Being able to look at the sites while simply listening to the audio can make it more enjoyable then staring at a phone, she says. Overall, touring with apps rather than hiring guides, can save travelers from $60 to $100 per day, Bowen estimates.

Favorite Country App: Rick Steves' Audio Europe

Cost: Free

Walking tours detailing Italy's not-to-miss sites such as the Colosseum and Sistine Chapel in Rome are a favorite for Annie Fitzsimmons, a travel writer who contributes to magazines like Travel and Leisure. "The app is so pretty and easy that you don't have any question on where you need to go next," she says.

The app is split into tracks of landmarks and neighborhoods, so it's easy to combine tracks for a custom tour of each city. The walking tour app offers tours in other European countries, including France, Spain and Germany. A walking tour of the Palace of Versailles near Paris also made touring the giant estate more manageable, Fitzsimmons says.

Favorite National Park App: National Parks by National Geographic

Cost: Free

Navigating hiking trails and sites can be tiring and confusing, especially when exploring vast national parks. But when Fitzsimmons didn't want to splurge on a guide, which can cost more than $50, she used National Geographic's National Parks app to tour the Grand Canyon. The app also contains information for 20 of the most popular U.S. national parks, including Yellowstone, Yosemite and Badlands, and lets users download park-specific guides.

"Arizona is my home state and it gave me new insight into the park," says Fitzsimmons. (The Grand Canyon also offers short cell phone audio narrations on various points of interest.)

Note that all the park "secrets" and photo-taking tips can drain a battery in such an expansive space. Fitzsimmons uses the Mophie, a rechargeable external battery that doubles as a case for her iPhone.

(Follow us @ReutersMoney or here. Editing by Beth Pinsker Gladstone and Dan Grebler)

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