The Roman Forum sits between Plaka and Monastiraki. It was built in the 1st century AD as an extension to the older Agora. As with some other archaeological sites in Athens, it’s easily seen from outside the fence, but there are a few interesting structures inside the complex worth getting closer to. Admission is €6 as of July 2016, but a €30 combo ticket allows access to several other archaeological sites in Athens, including the Acropolis.
One of the most important buildings in the Roman Forum is the Tower of the Winds. It was built in the 2nd century BC as a weather vane and water clock, replacing the older, simpler water clock in the Agora. On the top of each side are friezes representing the eight winds. In the 18th century, under Ottoman occupation, it was used by Sufi whirling dervishes as a monastery to perform the Sema ritual.
Another important building is the Fethiye Mosque, an Ottoman mosque built in 1456 to honor the visit of Sultan Mehmet II’s visit to Athens. It was used as a barracks in 1824, and in the 1880s to 1935 as a flour storeroom for a military bakery next door. It’s not open to the public, but you can get up close to admire the craftsmanship.
Also inside the fence, you can get an up-close look at the public latrines, a few columns, and the Agoronomeion, which was a public building that was probably used for worship of the emperor.
Outside the Roman Forum, across from Fethiye Mosque, you might notice a ruined doorway standing among some trees. This was an Ottoman madrassa, an Islamic school built in 1721 by Mehmet Fehri. In 1833, it was used as a prison. It was destroyed in 1914.