Omonia Square (Plateia Omonias) is the center of Athens, and is composed of the actual square together with the surrounding streets, open areas and assemblage of grand buildings that include banks and offices. The neighboring area of Exarcheia (Εξάρχεια) to the north, dominated by the Athens Polytechnic and its famous band of anarchists, is a bohemian district with lots of bars and clubs visited by students, intellectuals and people who are into alternative culture.
Omonia is the exact opposite of its neighbours Plaka & Monastiraki as there is no classical attraction in this multi-cultural area, however it's where you go for cheap eateries, exotic imported goods and food and basically day-to-day items at affordable price.
Athens Art Gallery (Pinakothiki), Pireos n° 51 (Koumoundourou Sq), ☎ +30 210 3231841. M-F 09:00-13:00, 17:00-21:00. Paintings of Greek painters of the half XX century are displayed.edit
National Archaeological Museum of Athens - This is the largest and most popular of Athens' many museums, and is usually very crowded. Its vast collection includes treasures unearthed from Mycenae by Heinrich Schliemann; a staggering array of sculpture including the earliest known Greek figurines dating from around 2,000 BC; frescoes from the volcanic island of Santorini; as well as remains of Antikythera mechanism, the oldest known mechanical computer; and so much more that it is recommended visitors make several visits to absorb it all. To get here by metro, it is better to use the Victoria Station (one station north of Omonia Station) and walk down 28th October Street.
Beware of an annoying fact: there is only one ATM on Omonia square, in the metro station, and belonging to the National Bank and its interface is only displayed in Greek.
Asian shops: from Monastiraki, just walk down Athinas street. On side streets such as Evripidou and Sofokleous, you'll see many Chinese, Arabic or South-Asian shops which are interesting for spices and basically all kind of imported goods that are inexistent or quite expensive in Greek shops. Beware people are usually not fluent in English.
Wan Tya Fù (Chinese Supermarket), Keramikou 31-33 (From Omonia sq., take Pireos str. then Voulgari str. or any side street after), ☎ 6993889588. The best shop in Athens to get Chinese teas, spices, noodles etc. at good price. The staff speaks Greek (and obviously, Chinese) only, but is welcoming.edit
If you are, for instance, a student settling down in Athens and wanting to save some money, Athinas Street is great to get all the basic stuff you may need, from cheap cloths to cooking and bathroom accessories.
Barba Yannis, Emmanouíl Benáki 94, ☎ +30 210 3300185. Old fashioned simple taverna, popular with students and working people; seems to be always open.edit
Lefka, Mavromiháli 121, ☎ +30 210 3614038. Closed Su. Some would put this place technically in Neapoli rather than Exarcheia. It's a traditional taverna with spacious outdoor seating that's been around forever. edit
Ideal (also spelled Inteal), Panepistimiou 46, tel. +30 210 3303000. A restaurant where local employees go during lunch break, therefore try to go before the closing of the offices.
Rosalia, Valtetsiou 58, - Exarxeia, tel. +30 210 3302933. A tavern that serves simple plates in the purest Greek tradition.
Yantes, Valtetsiou 44 - Exarxeia, tel. +30 210 3301369. A tavern with a garden. It serves organic dishes.
Salero Bar Restaurant, Valtetsiou 51 (Exarcheia), ☎ +302103813358, . daily 1pm-2am. Specialties from the Iberian Peninsula and the Mediterraneo. Cozy environment with spacious backyard. Bar that serves until late, too.edit
Athens House. It has a great kitchen that is surprisingly well equipped with double stove top, heaps of pots and pans, plenty of plates, cutlery and ample fridge/freezer space. The rooms are extremely clean and tidy, some have TVs. Free, very fast and reliable WiFi in all rooms. One terminal is located in the common area, but it is also used by the receptionist and she may be hesitant to give it up. The toilets and showers are clean, although the showers are rather small and the hot water isn't completely reliable. Travellers should be advised that in the Omonia area street prostitution and drug dealing/use is common place, particularly in front of this hostel. Although this activity poses little danger to tourists (unless you're indebted to them!), it may be confronting to some people.€10 per person for 4 bed shared accommodation, €25 for 3 bed private rooms. edit
Hostel Aprodite (Aphrodite), 12 Einardou and Michail Voda corner 65, ☎ +30 210 8810589 (email@example.com), . Low-budget backpackers' hangout not too far from Larissa train station and Victoria Square, a bit north of the Omonia district.€12 for a 6 bed dorm, €14 for a 4 bed dorm, and more. Air conditioning €3 extra per person. edit
Arta, Nikitara St (few steps NE from Omonia), . €35 double with ensuite, discounts available. edit
Hotel Elite Athens, 23 Pireos St, ☎ +30 210 32 25 891. Located 10 minutes away Monastiraki; simple, decorated rooms with air conditioning and television. There is also a bar and coffee shop on the ground floor.edit
Elysium (BestWestern chain)  firstname.lastname@example.org. Cheap-and-chic boutique hotel, 16 rooms. For those needing official booking confirmation for arrangement of visa, the only way is to book via the BestWestern official website.
Zinon (BestWestern chain)  Decent choice when everything else booked in advance: huge and impersonal hotel; quite old building with recently refurbished interiors and western management results in low rates and a good service. But it's Omonia--don't plan to leave your room in evenings, it's quite dirty and the only Russians-run food outlets are nearby. Travellers mix: majority are elder, retired people (and families) from US / Canada / Australia.Internet connection is declared to work for every room. WiFi is good strength but very unstable. LAN outlet is in every room--but not supported, according to reception (and not tried). Single €60, double €80 (breakfast included). For those needing official booking confirmation for arrangement of visa, the hotel itself can't provide it--you can only print email confirmation of booking from BW chain's global web site.
Fresh Design Hotel A superb designer hotel within easy walking distance of the Acropolis in the centre of Athens. The rooftop bar and swimming pool has breathtaking views of the Acropolis - the perfect way to end the day's sightseeing or business. Online booking.
As a visitor, you may be encouraged by Athenian people to avoid Omonia area especially at night, however the neighbourhood is intensively patrolled by fully equipped anti-riot units, or at least on major intersections.
Omonia is notorious for pickpockets and prostitutes, so keep an eye on your belongings.
There are many people who use drugs in the open even during the day and can be a harrowing site for those not used to it. It is strongly advised not to bring children here for too long. Particular places to avoid are roads right of the National Archaeological Museum and the south end of 3 September St.
More recently, Sofokleous St (a major street south of Omonia), especially the western part near Pireos St, has gotten a reputation for crime and drugs.