If it's the Marriott Hotel located Leof. Andrea Siggrou Street, you will be very far from the usual interesting sites in the center of Athens (Acropolis, Plaka, Syntagma Square, etc) but right in front of the Stavros Niarchos Foundation Cultural Center which is interesting to see and visit and where there is a great park
The Academia hotel is closer to the center but not very well located either, almost 2 km from the Acropolis.
On the other hand, it is very well placed if you want to see some street art in the Exarchia district or go to Lycabettus Hill.
I'm sure you can find better and more convenient for you, and other forum members will be able to advise you some other places.