Büyükada, the largest island off Istanbul in the Sea of Marmara, has been inhabited by humans for, I suspect, at least a couple of thousand years. So it is inevitable that there will be some really old houses on the island, although none is that old. We passed by this one on our way to the more remote corners of the island and the Monastery of Aya Yorgi. We couldn't quite tell if the house was still occupied (now as I examine the picture, I see what may be curtains in the upper windows).
The surviving old houses of Istanbul, usually from the early 20th century, sometimes have elaborately shaped large knockers on their doors. This one was no exception.
We have to remember that these houses were built long before there were such things as electrical door bells. One had to knock hard on the door if one wanted to be heard. Hence, a large knocker lessened wear and tear on one's knuckles. They may also have been status symbols.
We didn't think of testing the effectiveness of these knockers.