Students from EU countries may enter many sites for free. Students from other countries have their entrance fees reduced. So take your International Student Identity Card with you.
For those interested in learning modern Greek, there are several schools offering courses in language instruction for foreigners. Most of these are designed for English speakers, but some schools have courses for people with other first languages. Some schools are in Athens, some in Thessaloniki among them the very good school of Modern Greek language in the Aristotle University of Thessaloniki while others have centers in the islands offering a residential program that combines language study with a vacation. Some offer individual tutoring in addition to classes. Some well established programs are The Ikarian Centre (http://www.greekingreece.gr/), The Hellenic Culture Centre (http://www.hcc.gr/) an associate of The Ikarian Centre, and The Athens Centre (http://www.athenscentre.gr/).