I am reading Christopher Day's Spirit and Place - a wonderful book by one of my favorite designers.
It reminds me of an intuitive sense I have about timeless buildings. They seem to share several key characteristics.
Timeless buildings tend to be close to nature - in materials and design. They use natural or less processed materials. Their forms often reflect/mirror organic forms - including those of the local landscape. They draw attention to community and nature (not to the design/designer).
For these reasons and more, we are likely to experience these buildings as nourishing and appropriate to place.