The ancient poplar wood door is "solid and elegant" with well-preserved hinges and a "remarkable" design for holding the boards together, chief archaeologist Niels Bleicher said Wednesday.
Using tree rings to determine its age, Bleicher believes the door could have been made in the year 3,063 B.C. around the time that construction on Britain's world famous Stonehenge monument began.
"The door is very remarkable because of the way the planks were held together," Bleicher told The Associated Press.
Harsh climatic conditions at the time meant people had to build solid wood houses that would keep out much of the cold wind blowing across Lake Zurich, and the door would have helped, he said. "It's a clever design that even looks good."
The door was part of a settlement of so-called "stilt houses" frequently found near lakes about a thousand years after agriculture and animal husbandry were first introduced to the pre-Alpine region.
It is similar to another door found in nearby Pfaeffikon, while a third found in the 19th century and made from one solid piece of wood is believed to be even older, possibly dating back to 3,700 B.C., said Bleicher.
The latest find was discovered at the dig for a new underground car park for Zurich's opera house.
Archaeologists have found traces of at least five Neolithic villages believed to have existed at the site between 3,700 and 2,500 years B.C., including objects such as a flint dagger from what is now Italy and an elaborate hunting bow.
Helmut Schlichtherle, an archaeologist for the conservation department in the German state of Baden-Wuerttemberg, said finding an intact door was very rare, as usually only the foundations of stilt houses are preserved because they are submerged in water for millennia. Without air, the bacteria and fungi that usually destroy wood in a matter of years can't grow, meaning many lakes and moorlands in Europe are considered archaeological treasure troves.
"Some might say it's only a door, but this is really a great find because it helps us better understand how people built their houses, and what technology they had," he said.
Schlichtherle, who wasn't part of the Zurich dig, said over 200 stilt houses have been discovered in southern Germany alone, but to date no doors.
The Zurich scientists plan to exhibit their door once it has been carefully removed from the ground and soaked in a special chemical solution to prevent it from rotting.