The Athenian Acropolis is the ancient "high city" of Athens, a prominent plateaued rock perched high above the modern city with commanding views and an amazing array of ancient architecture, mostly from the Classical period of Ancient Greece, the most famous of which is the Parthenon. A visit to Athens is not complete without visiting the Acropolis - hundreds of tourists each day accordingly make the pilgrimage.
The Acropolis of Athens is open daily. Summer opening times: 8AM-7PM, Winter opening times: 8AM - sunset. Telephone: +30 210 3214172. Get there as early as possible to avoid heavy crowds, and summer heat if relevant.
General admission is €12 but excellent concessions are available, as is free access to many categories of individuals, especially under-18s and European university students - check the official web site . There are also a limited number of free days for the public listed each year; again, check the website.
The entrance to the Acropolis is off Theorias Street. From the Akropoli metro stop and New Acropolis Museum, walk west along Dionysiou Areopagitou Street and take the first left on to Theorias; from the Thissio metro stop west of Monastiraki, walk west to Apostolou Pavlou Street, turn left on it, and walk south to turn left on Theorias. From Plaka, you can walk south up steep Mnisikleous Street as far as you can go and turn right on Theorias.
The main archaeological site is surrounded by a large public area, a plethora of trees with beautiful stone-paved paths (designed by the great Greek architect Pikionis). A canteen with a wide range of food and drink is reached before you get to the ticket kiosk - but beware: refreshments are available only at exorbitant prices. You will definitely need a bottle of water with you in the hot summer, so either bring it with you or buy it from the kiosk on Dionysiou Areopagitou Street, just outside the entrance. There are water fountains within the site, but the water isn't always cold. Guides can nearly always be found offering to show you around - at a price - at the point where tickets are checked. An alternative will be a printed version of this article (info not yet added), or ask for the free leaflet published by the Archaeological Resources Fund (includes a ground plan of the site and valuable information on the various monuments).
Following European regulations, disabled access to the Acropolis can be gained by means of special paths and a purpose-built lift  on the north face of the hill. Apparently this is only for the use of those in wheelchairs.
For students of the European Union, entrance is free.