Next week is National Park Week. From April 21-29, all 397 units of the park system will waive their entrance fees, from Acadia to Zion and everywhere in between.

To help celebrate National Park Week, mobile app developer Chimani has announced that it will give away 1 million of its 10 highly rated park guides for smartphones. Normally they cost between $4.99 and $9.99 each. If you’re considering a trip farther off the beaten path, their general guide for national parks is also free. All are available for iPhone and Android using the links on their website.

If you use an iPhone, NPCA has a free National Park Field Guides app.