The caves are host to a library of Kryptonian information that can only be accessed by placing the octagonal key into its keyhole. In addition to the wide shot of the keyhole as it originally appeared in "Skinwalker," here are more shots of the keyhole to show details.
First, this is one of the first closeup shots of the keyhole mechanism, and it looks distinctively different than it does at other times. In this version, none of the symbols surrounding it are particularly legible.
An even closer look at the keyhole:
The drawings around the keyhole changed after Clark put the key in the keyhole.
The symbols are surrounding the keyhole are definitely Kryptonian, but their exact meaning is up for debate. The symbols in the outermost ring are composite symbols, similar to the "hope" symbol and are, as a result, impossible to translate. The inner ring, however, is somewhat easier to translate, although its ultimate meaning is still mysterious. Starting at the top, there is what appears to be an S, an M, a T, an O, the symbol for "hope," another M (or possibly an H, depending on which way is "up"), another T, a P (or possibly an F?), and what looks like another T. It would be nice if these symbols spelled out something intelligible, but it sadly seems as if it is not meant to be.
The keyhole again changed from the rather crude drawing in the above picture to a neater, more professional-looking version.
The symbols in the outermost layer look similar to those engraved on Palak. The symbols on the middle ring aren't like any that appear anywhere else in the show.
The keyhole changed yet again to this configuration after Walden meddled with it at the end of Season 2. The inner two rings seem to be the same, but the outermost ring with Kawatche symbols is gone, and there are lines of Kryptonian symbols radiating outwards like sunbeams.
It is difficult to determine exactly what the lines of Kryptonian say as a lot of it seems to be composite symbols rather than individual letters.
