Some of the most incredible features of our national parks are hidden beneath the surface.

What's underneath the national parks
Credit: CuriosityStream

The National Park Service celebrated its 100the birthday on Thursday. And while most of us think of the vibrant red canyons in Zion or the sheer face of Yosemite’s Half Dome, the most iconic parks are only the tip of the iceberg.

To celebrate the centennial, CuriosityStream is presenting a seven-part documentary series on the “Underwater Wonders of the National Parks.”

“Everyone talks about the vistas, or they talk about the hiking and the camping,” series producer Jorge Franzini told Travel + Leisure. “I’ve never heard anyone talk about the [areas] hidden beneath the surface.”

Franzini and his team scoured the country for six of the most fascinating underwater locations that are managed and protected by the National Park Service’s Submerged Resource Center. The “Underwater Wonders” series highlights the geothermal smokers of Yellowstone—the likes of which are typically only found deep down on the ocean floor.

What's underneath the national parks
Credit: Wikimedia Commons

In other episodes, they explore the wreckage of a B-29 bomber in Lake Mead National Recreation Area, the leech-filled sinkhole at Arizona's Montezuma Castle National Park, and Death Valley’s Devil’s Hole.

What's underneath the national parks
Credit: Gina Ferazzi/Getty Images

“It’s literally this crack in the middle of the desert,” said Franzini, describing Devil’s Hole, “And it’s home to 120 of the rarest fish in the world.”

This spring-fed pool is an oasis in the Mojave, and the 93 degree waters are home to the few remaining, iridescent blue Devil’s Hole Pupfish.

Over the course of two episodes, we explore the USS Arizona and see early efforts to map the previously uninvestigated lower floors. And as far south as St. Croix in the U.S. Virgin Islands, scientists let us share in their search for two 18th-century slave ships submerged just offshore.

What's underneath the national parks
Credit: Steve Simonsen/Getty Images

In a statement, Deputy Chief of the NPS Submerged Resource Center Brett Seymour said: “The national parks belong to all of us, and now for the first time millions of viewers have the chance to see what even park visitors rarely [can].”

“People just don’t know about [these places],” Franzini said. “And they need to know not just that we can go there and enjoy them, but that there’s so much hard work done to maintain these sites.”

Even if you don’t have a CuriosityStream membership, you can watch the “Underwater Wonders” series—in all its high definition, 4K quality with a 30-day free trial.

Melanie Lieberman is the Assistant Digital Editor at Travel + Leisure. Follow her on Twitter and Instagram at @melanietaryn.