The administration of the Spanish capital, of course, approaches this project very seriously, since a lake of such dimensions, and in a public park, is certainly not easy to clean. The last time this happened was back in 1982.

Over the decades, the pool has collected many strange objects that piled up at the bottom hidden in obscurity. They range from common things that people could afford to throw away or drop to unexpected finds.

In 2017, the Madrid City Council decided to make public some of the "treasures" they found at the bottom of the lake. Among them, however, there was a femur, too, which stirred panic in many. Police started investigating to see if that was human remains. However, it turned out to be a cow bone. Which was also a mystery, how it ended up in a lake in Madrid.

Among the items found were even weapons and ammunition, but even that was easier for officials to explain than cow bones. The strange finds continued. A personal computer was also taken out, which hardly got there by accident. So many phones from different years were found in the lake, the bottom looked like a museum of technology and its development. Hundreds of chairs, purses, urns were found, most likely from scattering of the ashes of deceased family members.

When will the next cleaning take place and what wonders will the Spanish find then? We do not have an accurate answer, but if we follow the logic and apply the 35 years between the two cleanings of the lake in 1982 and 2017, then the next one will be in 2052.