Jiekai Z.
Google
This is an inexpensive and no-frills place to stay. As long as you have appropriate expectations this place is amazing.
The rooms are small, there are shared bathrooms and showers, but the A/C works well and room service provides clean toiletries and towels everyday.
The highlight of this hotel is the location. This is in the middle of ALL the popular attractions and neighbourhoods commonly recommended in Athens. It is also in the middle of a very lively and bustling part of Monastiraki which gives you plenty of options to explore, socialize, and have fun. It's also near 2 major train stations.
The staff are also VERY kind and warm-hearted, and were very helpful in arranging a taxi for me to the airport.
One note however, there is only a lift for luggage, not for people. You will need to go up & down flights of stairs to get to your room. I was on the 5th floor, and it was a mini workout each time, but seeing how much food I ate, I needed it.