Istinye Park is a large shopping centre in Sariyer, north of the city centre, with roughly three hundred shops including a separate luxury wing.
Practical notes: open daily 10:00 to 22:00. There is a cinema, a supermarket, a covered-bazaar style food hall and valet parking. Tax-free refund forms are issued at the information desk on the ground floor — bring your passport.
Getting there: taxi is simplest, around forty minutes from the hotel depending on traffic. Public transport requires the tram plus a metro connection and takes over an hour, so it is rarely worth it.
If your time in Istanbul is short, the bazaars and Nisantasi are both closer; Istinye Park makes sense mainly if you want specific international brands under one roof.