On the south side of the National Archaeological Museum, this is an important collection of Greek inscriptions, but the main halls' tersely labeled shelves of stones are uninspiring to the casual visitor. Two newer sections, however, give some background on the Greek writing system and show off the most historically revealing pieces, such as a third-century copy (or perhaps forgery) of the decree ordering the evacuation of Athens before the 480 BCE Persian invasion.
To decode some of the writing yourself, ask the staff for a sheet of ancient alphabet variations.