Monica's apartment is excellent for exploring Berlin. The location is perfect – right on Alexander Platz; many places are within walking distance, and for the rest you have the AlexanderPlatz station for a convenient transportation wherever you need in the city or outside, including direct train from the airport.
The room is not big but it's comfortable, with separate entrance and private bathroom, so it gives you real privacy when you need it. Although it is located on a very busy street, it is very quiet as the apartment is on the 9th floor and the room is in its back. The only noise was from the trains going to and from AlexanderPlatz station, but I guess this is true about many places in the city and you get used to it.
Monica, Ivonne and little Josephine were lovely and accommodating hosts, and made everything to let me feel at home. They certainly made me want to come back.