Get off at Panepistimiou station. Exit National Library. It's a 25 minute walk. The easiest is to walk up Ippokratous all the way for a while until you reach house number 172 on your right which is a Gyros restaurant called Ψητοσυνάντηση. Just before that, turn right into Digeni Akrita. When you see the flower store at the corner, go up the street right next to it which is Valsamonos. House number 10/12 will be on your right.
Get off at Ambelokipi station. It's a 10 minute walk. Cross the large street which is Leoforos Alexandras and walk west. Turn left into Asklipiou. Turn slightly left into Grigoriou Theologou, then left into Valsamonos. House number 10/12 will be on your right.