This mysterious sculpture is entitled "Antipodes" (Sam Sanborn, 1997) and it stands the garden outside the Hirshhorn Museum. This Arts Observer article provides a good description of the piece with nice images of the work.
A detail of part of the sculpture reveals of pattern of letters. Reading across the top row of this photograph you can just make out the word KRYPTOS; this word is repeated in every line in a slightly different position, surrounded by what appears to be the other letters of the Roman alphabet: ABCDEFG ... etc.
I took at look at the other half of the sculpture (left-hand side in this photo), which looks like the letters of some Cyrillic script in reverse. I have no idea what's going on here. But -- as it turns out -- someone else has devoted years studying this artwork and has finally (as of September 2003) cracked parts of the code.
The English part of the sculpture, by the way, apparently repeats the code in another sculpture by Sanborn entitled (appropriately enough) "Kryptos," and this artwork stands on the grounds of CIA Headquarters in Langley, VA.
