Construction workers in Belgium made an extraordinary discovery this week, uncovering an estimated $10.4 million worth of gold while installing a new sewer beneath a former brewery.

Police in Sint-Gillis-Dendermonde, a Flemish community outside Brussels, said the workers immediately alerted authorities after discovering the gold during excavation work.

Officers documented and catalogued the find before transferring it to a high-security federal government vault for safekeeping.

An 18-year-old construction worker named Kobe told Belgian broadcaster VRT that he initially mistook the gold pieces for one-euro coins.

“Our first reaction was actually disbelief, surprise,” he said. “Of course, we didn’t expect to find gold.”

Kobe said the crew had been removing part of an old foundation to make way for sewer pipes when they noticed unusual objects buried beneath the structure.

“When we did that, we suddenly saw something lying around,” he said.

Project leader Mario described the discovery as a “crazy feeling,” saying workers began shouting that they had found gold.

He went to inspect the discovery himself and initially handled some of the pieces before workers continued digging and uncovered additional coins and gold bars.

“Only then did what we had found really dawn” on them, Mario said.

He immediately contacted his supervisor before notifying police.

Authorities are now expected to investigate the origin and ownership of the multimillion-dollar cache, including how the gold came to be concealed beneath the former brewery.