NPF - National Park Finder, is a unique app that allows you to search for national parks all over the United States that conform to your needs.
Part I - Search: You can perform the following searches -

1. You want to visit a place where you can go Horseback riding or kayaking?
2. You want to go to a park where you can see Bisons, Elks, and Wolves?
3. You want to go to a park where you can bird watch Condors, Starlings, and Roadrunners?

Your answer is NPF. This app will display all the national parks that fit your criteria.

Part II - Image viewing.
Once you locate a park, you would want to see the images of this park. This app uses Flickr Api to bring to you a comprehensive list of beautiful images. You simply tap the pushpin and you can flip through these images.

Part III - Directions.
You may also want to navigate to this park and get going! If you click the “Directions” toggle, and tap the pushpin, this will show you a route from your current location to the park, and also provide you detailed itinerary steps.