Travelling to Delphi? Book a private transfer with a Greek driver who has done the Athens → Delphi route hundreds of times. The drive is 2h 30m each way via the E75 and E65, climbing through pine forest and ending with the spectacular descent into the Pleistos river valley with the Gulf of Corinth glinting in the distance.
Delphi works beautifully as a one-day round-trip from Athens. The standard Luxi day-trip pattern: morning departure 08:00, arrive at the archaeological site by 10:30, 2–3 hours at the temple, treasury and museum, lunch in Arachova (the photogenic mountain town 15 minutes east), return to Athens by 18:30. A sedan day-trip is €280–€340, a van €340–€400 — comfortable for four to seven passengers.
The site itself is on the southern slope of Mount Parnassus, 600 m above the valley. There's no public parking close to the archaeological zone in summer — your driver will drop you at the entrance and meet you at the agreed time, which removes the single most stressful part of the day if you tried it self-driven.
For accommodation, most travellers either day-trip from Athens or overnight in Arachova (ski resort in winter, cool retreat in summer) or in the modern village of Delphi (walking distance to the site). One-way transfers from Athens are €180–€220.
For the historical context — what the Oracle was, why this hillside, what the Pythia actually said — see the Delphi glossary entry.