To me, one of the most fascinating design elements the Greeks used was entasis. (had been used by other great builders e.g Chinese)
The columns are slightly convex at the center top third. That makes the columns look visually straight when viewed from a distance (as opposed to looking like they were tipping over backwards at the top).
And we didn't know how stonemasons applied the convex curves, with radii hundreds of feet long, to columns 34 feet high until recently. Scaled curve guides were found engraved in stone with horizontal distances ticked off for each column section against greatly foreshortened vertical distances.
The bulk of the temple was designed by Phidias, who also did the statue of Zeus. John Romer in his 7 wonders of the world does a wonderful job of laying out the temple design and what a marvelous architecht Phidias was.