Marin's place is super cosy and nice, the terrace alone is amazing, the perfect place for breakfast or even some evening drinks with friends!! The apartment is super close to the Central Station (about 10 mins walking), from there you can basically go anywhere in Milan. We found the public transport there super reliable, so from the Centrale is about 5 stops to the City Center where the Duomo and the Gallery are.
If you are walking back to Marin's place from the Central Station I recommend getting ice cream at "Antica Gelateria Sartori", which is just outside the station, they honestly have the best ice cream I have ever tasted in my life.