Delphi was the sacred center of the world for the Ancient Greeks and undoubtedly a remarkable achievement of purposeful architecture, a sanctuary built into the challenging landscape to inspire awe and worship. Unfortunately, very little is left of its former glory, and the visual impact is fairly muted. After experiencing grandiosity of the Parthenon at Acropolis or the vastness in various states of preservation at Delos, it is hard to see Delphi as little more than a sequence of terraces with few surviving features here or there. Of course, you may be more into archaeology than I am or simply more attuned to the aura of the great legacy that the Ancient Greece bestowed on the mankind, so the simple fact of being in such an important and symbolic place may give you additional satisfaction.
Some of the remaining features are definitely impressive.
The only standing building is actually a reconstruction carried out at the beginning of the last century. This is the Athenian Treasury, not a temple, but as the name suggests, the place housing the votive offerings to the sanctuary. It stands along the main path to the Temple of Apollo, the Sacred Way, so anyone ascending here would be able to take a glimpse of the treasures and to reflect whether they had to make their own offerings.
A few terraces higher is the theater.
The focal point of Delphi is the Temple of Apollo. The earliest temple on this site was built in the 7th century BC, but the remaining columns date to about 300 years later.
The bronze column on the left is a very recent replica of the Serpent Column, a storied military trophy that was offered to the Delphi sanctuary in 478 BC. The original has been relocated to Constantinople in 324 AD, and the replica built only in 2015.
The Temple of Apollo is undoubtedly photogenic, backed by the views over the valley of Phocis. Here are various angles.
Upper terraces provide even more sweeping views.
Delphi is located in the administrative region of Central Greece about two and a half hours drive from Athens. An hour appears sufficient to explore the core of the site, but if you decide to climb higher, to the stadium and beyond (of interest only if you want to do some hiking, in my humble opinion), you may have to add another hour or more. The archaeological museum is a short walk from the site by the main road and is accessible for a separate fee (or on a combo ticket); allow one more hour if you want to view its collection.