To call Hartung Park a secret would be a stretch, but the park, which opened in spring 2010 on part of the old Hartung Quarry site is tucked away along Menomonee River Parkway in a residential neighborhood between Burleigh Street and Capitol Drive.

Though its footprint is not huge, the park -- at the corner of Keefe Avenue, on the edge of Tosa and Milwaukee -- is packed with amenities and so it’s easy to see why it has quickly become a neighborhood favorite. But if you didn’t live nearby, you might not even know Hartung Park exists.

Tosa farmer Frederick Hartung began quarrying the land in 1910, digging out the dolomite that was used in building homes and businesses around the area, including the tower at nearby Mount Mary College -- which can be seen above the trees from the paths that run through the park.

Roughly three million tons of rock were pulled out of the pit that went nearly 100 feet into the ground.

The quarry operated on the site until 1961, but the scar remains in the Earth in the rise adjacent to the park. A fence keeps the curious from falling in, though there has been talk of expanded the park beyond that line.

In 1964, the City of Milwaukee began to fill the hole with trash, though in later years only clean fill like concrete and soil was dumped there.

Skip ahead to 2005 and a group of neighbors formed the Hartung Park Community Association to create the park.

Now, there is a pond, a large mowed grass area, paths that stroll through prairie grasses, a super-fun playset (with bongos!) and, along the trails, a stone labyrinth.

A couple tables are often occupied by picnickers or folks watching their kids play. Along the playground are a series of panels that explain the history of the land, the story of the quarry and trace the birth of the park.

Just above this is a slope that is dotted with sculptures of the sorts of creatures that would’ve lived at Hartung Park when it was covered by an inland sea and the slope was part of a warm water inter-reef basin.

"Fossil evidence shows that the area was teeming with life, supporting diverse animal and plant communities," notes one of the panels. "Clinging to the bordering reefs, coral blooms of all shapes and sizes flourished. ... The low-energy nature of the inter-reef basin provided an ideal environment for the deposition, and eventual preservation, of many organisms upon their death. As a result, fossilized specimens of multiple Silurian-aged animals and plants have been discovered at Hartung Park."

The stone here comes from two geological formations: the Oak Creek and Racine formations.

According to one of the panels, it is the trilobites in latter that is of the greatest paleontological significance.

"Containing one of the most diverse Silurian Period trilobite collections in the world, Hartung’s bedrock is known to exhibit fossils of over 20 species of trilobites. The abundance of Wisconsin’s state fossil, species Calymene celebra, in certain Hartung strata is legendary. Fossil collectors reportedly found as many as 100 complete trilobite specimens in a day."

Many of them are represented not only by the sculptures in the park, but also in impressions left in the concrete that surrounds the playset.

When kids see them, they’re delighted. Though, I admit, some are considerably more delighted by the hanging and spinning options on the cool playset.

If you’re looking for a special occasion to visit Hartung Park, the green space hosts a weekly farmers market on Wednesdays from 4 to 7 p.m., June through September. Along with vendors, including the Bubble Tea Fusion food truck, there’s live music and entertainment.