If you plan to stay in Lavrio there is plenty cafes and restaurants all within walking distance and some located on the water. There is also a port that has a ferry that can take you to two nearby islands. They are called Kea and Kythnos.
If you are staying in Athens you can get to and from Lavrio by train, bus, or taxi if you do not want to rent a car.
Temple of Poseidon
Sounion, 195 00, Greece
There is a cafe/restaurant under the shade to enjoy the beautiful view. It is very windy so be prepared. Also very beautiful spot during sunset and when there is a full moon.
Acropolis
Athens, 105 58, Greece
You will need to buy tickets in advance to arrival.