What top 5 must sees

Here's a good page to get you started with your research, and then feel free to come back for more specific questions. :-)

https://www.ricksteves.com/europe/greece/athens

It depends on what your interests are, but I would suggest:

1) Acropolis (buy tickets in advance)
2) Roman Forum
3) Panathenaic Stadium
4) National Archeological Museum
5) Walking around Plaka neighborhood or the National Garden

The Temple of Olympian Zeus is currently covered in scaffolding, so that's not worth seeing.

Here are Rick Steves’ recommendations:

▲▲▲ Acropolis The most important ancient sight in the Western world, where Athenians built their architectural masterpiece, the Parthenon.

▲▲▲ Acropolis Museum Glassy modern temple for ancient art.

▲▲▲ Ancient Agora Social and commercial center of ancient Athens, with a well-preserved temple and an intimate museum.

▲▲▲ National Archaeological Museum World's best collection of ancient Greek art, displayed chronologically from 7000 BC to AD 500.

▲▲ "Acropolis Loop" Traffic-free pedestrian walkways ringing the Acropolis with vendors, cafés, and special events.

▲▲ Anafiotika Delightful neighborhood draped across the hillside north of the Acropolis.

▲▲ Temple of Olympian Zeus Remains of the largest temple in ancient Greece.

▲▲ Psyrri Vibrant neighborhood near the center, great for eating, exploring, and escaping other tourists.

▲▲ Benaki Museum of Greek History and Culture Exquisite collection of artifacts from the ancient, Byzantine, Ottoman, and modern eras.

▲▲ Museum of Cycladic Art World's largest compilation of Cycladic art, from 4,000 years ago.

▲▲ Byzantine and Christian Museum Fascinating look at the Byzantines, who put their own stamp on Greek and Roman culture.

▲▲ National Gallery Great art by this nation's top artists from around 1850 to the present.

▲ Mars Hill Historic spot — with a classic view of the Acropolis — where the Apostle Paul preached to the Athenians.

▲ Thissio Good neighborgood for food and drink, often accompanied by fine views of the Acropolis.

▲ Roman Forum and Tower of the Winds Ancient Roman marketplace with wondrously intact tower.

▲ Syntagma Square Famous public space with a popular changing-of-the-guard ceremony.

▲ Ermou Street Pleasant traffic-free pedestrian street brimming with international chain stores and fun people-watching.

▲ Church of Kapnikarea Small 11th-century Byzantine church with symbols of Greek Orthodox faith.

▲ Church of Agios Eleftherios Tiny Byzantine church decorated with a millennia of Christian bric-a-brac.

▲ Panathenaic (a.k.a. "Olympic") Stadium Gleaming marble stadium restored to its second-century AD condition.

▲ Central Market Fun and aromatic sensory adventure, with a mind-boggling assortment of food and local color.

▲ Museum of the City of Athens Former royal residence with exhibits about the city's 19th- and 20th-century history.

One of the best and often overlooked site is Keramikos Cemetery located in Thisseio area.

It started out as ancient Athens' pottery center but was transformed into a cemetery.

It's a peaceful area with a good amount of "ruins" left plus a lovely museum with artifacts from the site including many headstones with inscriptions describing the loss of a loved one.

While the cemetery is from Ancient Athens the loss of loved ones is felt no different then than it is now.

For me it is a must when in Athens:

https://ancientgreecewanderings.com/visiting-kerameikos-cemetery-athens/