Temple of Hephaistos
The Temple of Hephaistos is one of two original buildings in the Ancient Agora in Athens. The other is the Church of the Holy Apostles. Hephaestus was the god of metal working, craftsmanship, and fire; essentially the god of engineers, and I find it somewhat amusing that the building dedicating the engineer is the one that survived!
Actually the building was used far beyond its original purpose, including as a Greek Orthodox Church, which partly explains its well-preserved state.