Kerameikos is named after Keramos, son of Dionysios and Ariadne, hero of potters. The area was used continuously for burials from the 12th century BC for a thousand years. If you follow Ermou street down from the Monastiraki train station, you will easily find it on your right.
Within the site are the ancient walls of Athens and the Sacred Gate which was only used by pilgrims from Eleusus who used the sacred road to and from that site during the annual procession. Nearby is the Dipylon gate, which was the main entrance to the city, where the Panathenaic procession began and where the city’s prostitutes congregated so they could make themselves available to weary travelers. It was from this spot that Pericles gave what was probably his most well-known speech honoring those who had died in the first year of the Peloponnesian war.
Between the two gates is the Pompeion, where preparations were made for the Panathenaic procession which was in honor of Athena. The building was completely destroyed in 88BC, and a 3 aisled building called the Building of the Warehouses was erected in its place in the 2nd century AD. The church of Agia Triada is in the background. The Eridanos river which once passed through the Sacred gate still flows beneath the site. It was covered by the Romans. On the Street of Tombs, you can see replicas of the gravestones of some of Athens most prominent citizens.
There is a small museum to the left of the site entrance with some really nice pottery, sculptures and right next to it is a collection of pillars which used to be grave markers.
Texts and images sources: https://www.wikipedia.org/, https://www.visitgreece.gr/