While strolling through your neighborhood, you may have passed a Little Free Library. The tiny, dollhouse-sized structures are filled with donated books, and adorned with a sign that typically encourages members of the local community to “take a book, return a book.” On Saturday, May 21, you can celebrate the unique grassroots literacy movement—and build your own mini-library—at the inaugural “Little Free Library Festival” in Minneapolis, Minnesota, Smithsonian reports.

Held in the city’s Minnehaha Park from 10 a.m. to 4 p.m., the free gathering will offer book swaps, Harry Potter trivia contests, pop-up puppet shows, and an instructional workshop in building Little Free Libraries. (For a full list of activities, check out the festival’s website.) Participants can also help build 100 new libraries, which will be distributed among communities across America that don’t have immediate access to bookstores and books.

Today, there are so many Little Free Libraries around the country that it’s hard to believe that a Hudson, Wisconsin, resident named Todd Bol created the very first one in 2009. According to the Utne Reader, Bol’s late mother, June, was a schoolteacher who loved to read. While tinkering around in his garage, Bol decided to build an object in her memory: a tiny red schoolhouse filled with books. Bol propped the house on a post in his lawn, and invited people to “take a book, return a book.”

The tiny library ended up being so popular that Bol built a few more. Eventually, he started selling them, or giving them away. The literacy project quickly grew in scale, and once national news sources caught wind of Bol’s efforts, many communities across America wanted their own Little Free Library as well.

In 2012, Little Free Library officially became a nonprofit organization. Today, communities are invited to build their own boxes by hand and fill them with books, or to purchase one from Little Free Library's website. If you make a DIY-library, you can officially register it with the organization for a fee of around $43. In turn, you’ll be provided with an official charter sign and number, and your library will be added to the organization's world map online.

Little Free Library remains a grassroots institution. However, the Hudson-based nonprofit has become a global phenomenon in recent years. As of January 2016, there were more than 36,000 registered Little Free Libraries around the world, including in 50 U.S. states and more than 70 countries. There’s even a photo book dedicated to the movement, called The Little Free Library Book.

Want to build your own Little Free Library? Detailed instructions are available online. And for the latest on the “Little Free Library Festival," you can follow #LFLFestival on social media.

[h/t Smithsonian]