As gross as sewers are already, this 15 plus-ton block of fat is probably enough to turn the stomach of even the most seasoned sewer worker.Thames Water

A 10-ton 'fatberg' made up of solidified fat, wet wipes, sanitary items and household waste broke a sewer pipe this week under the West London neighborhood of Chelsea.

The congealed lump had to be physically removed from the sewer system and caused some $600,000 in damage, according to the Guardian newspaper.

While the 10-ton fatberg was gross, it wasn't as massive as the 15-ton fatberg (shown here) that clogged London's sewer in 2013.

Fatbergs demonstrate that as gross as we already know sewers to be, given that they're massive, man-made rivers of human waste, not everything that goes down the drain necessarily gets flushed away. Explore other shocking discoveries that didn't quite clear the pipes.

This hideous mass is actually a colony of tubifex worms.YouTube screengrab

In 2009, a YouTube video claiming to have found an "unknown life form" in a North Carolina sewer garnered millions of views as curious users ogled this hideous, pulsing mass.

The identity of the "unknown life form" was later revealed to be a a colony of tubifex worms, which are naturally found in sewage and pond sediment, according to Wired. The video clip made them look unnatural, however, possibly as a result of how the worms responded to the bright light from the camera.

An entire village was found at a sewer construction site in Iowa.University of Iowa

Human remains tracing back some 7,000 years ago were discovered by construction workers at a sewer project site, as reported by Fox News in 2011.

Further excavation work proved that an entire village had once occupied the area, making it among Iowa's oldest-known human settlements. According to a University of Iowa press release, more than 6,000 artifacts, including bones, arrowheads and spear points, among other objects, were unearthed at the site.

Grisly discoveries like body parts or decomposing bodies are tragically common.Getty Images

Not all human remains found in sewers are of archaeological interest. Sometimes, the findings are of police interest instead.

In Michigan, body parts from two different people were found in Warren and Sterling Heights, reported in March. All police know so far in the case is that both individuals were white women, though their identities are still a mystery.

These kinds of grisly discoveries, though always shocking, aren't uncommon for forensic investigators, unfortunately.

Capitalsaurus is the official dinosaur of Washington, D.C.Getty Images

If human remains thousands of years old can be found in a sewer, could dinosaur bones tens of millions of years old also turn up in these manmade tunnels?

In 1898, fossils of a dinosaur, later informally named Capitalsaurus, were discovered at the intersection of First and F Streets S.E. in Washington, D.C. One hundred years later, Capitalsaurus would be named the official dinosaur of the District.

A more recent discovery also occurred in 2010, when a pair of Edmonton municipal workers in Canada unearthed dinosaur bones believed to be 70 to 72 million years old, according to the National Post.

A Civil War-era cannonball was discovered 15 feet underground in a sewer in Indiana.Getty Images

The last shot of the Civil War may have been fired nearly 150 years ago. But last May, a Civil War-era cannonball turned up in a sewer in Cannelton, Ind.

Found by sewer worker Shawn Fulkerson, the cannonball is believed to have been fired by a Union gunboat defending a cotton mill in Hawesville from Confederate soldiers.

This baby was rescued after being trapped in a drain pipe in China.Getty Images

Earlier this year, a baby boy was discovered in a sewer pipe in China.

His mother, a 22-year-old woman who birthed the baby in a public restroom, lost her hold on the baby after delivery and he fell down a toilet drain, as NBC News reported. Rather than saying anything to authorities herself, she told a neighbor in the building that she heard crying in the pipes, and the neighbor then alerted police.

The infant, later known as Baby No. 59 after the incubator in which he was placed, managed to escape the ordeal unharmed and received a flood of interest from Chinese netizens looking to adopt the young boy. The mother was not charged with a crime, although the case did spark outrage in China.

Alligators in the sewers of New York City? Urban legend. Frozen alligator in the sewers of Cleveland? Fact.Getty Images

Urban legends abound of fully-grown alligators turning up in municipal sewers. While those stories are strictly myths, given that the large predators wouldn't typically be able to survive in such cold, cramped conditions, there is some small truth to the story.

And by small, we mean about 25 inches. Or at least that was the size of a nearly frozen alligator discovered by Northeast Ohio Regional Sewer District workers. They managed to rescue the tiny alligator, later named Jenni, who was undergoing rehabilitation and under quarantine at the Cleveland Metroparks Zoo's conservation education program.

Snakes don't belong down drains.National Park Service

Anyone who's ever owned a goldfish has gone through the experience of flushing a family pet when the time comes. When larger pets go down the drain, however, be it by accident or intentionally, they don't necessarily get flushed away.

In 2008, an Australian man discovered a nearly six-foot-long python crawling out of his toilet bowl, according to Reuters. The animal is believed to have strayed away from its original owner.

This jewelry display shows part of the loot recovered by authorities after a $110-million heist.Getty Images

Not everything that ends up down the drain is waste. Sometimes hidden treasure lurks in the most unexpected of places.

In 2011, nearly $24 million worth of jewelry was recovered from a Paris sewer. The valuables were thought to be part of a $110-million heist at American jeweler Harry Winston’s boutique just off the Champs Elysees, according to Reuters.