Slightly off the newly beaten path but near the Ancient Agora, Kerameikos is well worth a few hundred metres of diversion.
Athens’ cemetery from 12thC BC thru the Roman era, the place is calm and tranquilising. The walls and gates seep with history while funerary statues are varied and impressive, even though the originals are in the National Archeological Museum.
The Ceramic Museum in Monastiraki.
Voula is not a bad little beach if you’re desperate for sand and sea though not at all up to normal Greek island beach standards.
45 minutes by bus (or metro/tube and bus) from Athens’ Syntagma Square and you have to pay a few euros to get on to the beach, but it’s clean and well serviced and the water is clear and unpolluted.
Basic food facilities are available, but don’t expect anything ethnic or interesting and look out for pick pockets on the bus.