If we’re going to talk “timeless” I might recommend a read through Chris Alexander’s “A Timeless Way of Building” and its follow-up, “A Pattern Language”.

Alexander talks about the timelessness and beauty of buildings in terms of culturally-defined patterns—almost ‘design patterns’ but a bit more abstract—that are applied and repeated to create buildings and spaces that evoke a particular “feeling without a name”: something we all feel when a building feels alive and congruous with the actions that take place there. A beautiful building is symbiotic with its purpose, its surroundings, and the people who use it.

That’s sort of a gross oversimplification though. I really recommend checking it out. Though its focus is loosely on architecture, I’ve seen a lot of engineers and designers get excited about it and find applications to their own work.