Cool Map of Athens? oasa.gr/index.asp?asp=sitemap.asp
..pdf map of Athens bus, tram and everything routes?
Depending on where your centrally located Athens hotel is, Omonia, Exarhia, Pangrati, Syntagama or Acropolis areas, taking advantage of the metro can be done more or less readily!
On the map r the Green Line is the old electric train line while the Red and Blue lines recently opened in 2004. Click map to see larger. Notice how there is no one point where all three lines converge.
To get from the ATH airport to the port of Piraeus
you have to change lines in Monastiraki from blue to green.
The tricky bit to the Airport (ATH) Piraues Port route is that you have to change lines in Monastiraki other wise you will end up in Omonia. Omonia is the busiest station but not the most pleasant of them. Its an impersonal place with a international crowd and a Balkan undercurrent and where you want to keep your wits about you.
If arriving in Monastiraki by metro from the AIRPORT (blue line) you need to change lines to the Green line to reach Piraues. Both entrances are connected by an underground passage. This is necessary as there are two different kinds of trains converging here both with differing gauge track. If you take the electric train from Piraeus, Omonia or Kiffissia for example you will debouch right in the square from the building you will see below.
If, however, you take the Metro from Syntagma square or the airport you will either have to walk the underground passage to debouch in the square or exit directly onto Athinas Street and walk 1/2 a block to the square. This may be important for you to know if you have luggage to carry or when meeting friends in Monastiraki. So differentiate when telling your friends where you will meet. Simplest thing to do is just meet by the church outside the station in the square unless its raining which it hardly ever does in summer. You are going to be doing some small amount schlepping in Monastiraki like it or not. More below in Monastiraki its child's play really compared to other tubes, subways, T's and Bart's.