hi there!
i know i know u wanted to kill me because im so latee but guess what?im gonna hav an interrail trip so i hav learnt about these train from Thessaloniki to İstanbul,filia express,it leaves Greece at 19.37 arrives İstanbul at 08.07 still i suggest u to check it.also i suggest u to find some place to stay in Sultanahmet(very historical with Blue Mosque and topkapi palace...) or Beyoglu(if u like nightlife and music u'll love it there r 1836369363place to hav fun),they r very central and easy to access.i think u also need to see The Galata Tower (Turkish: Galata Kulesi), also called Christea Turris (Tower of Christ) by the Genoese and Megalos Pyrgos (The Great Tower) by the Byzantines, is located to the north of the Golden Horn,one of the city's most striking landmarks.Maiden's Tower (Turkish: Kız Kulesi), also known in the ancient Greek and medieval Byzantine periods as Leander's Tower (Tower of Leandros), sits on a small islet located in the Bosphorus strait off the coast of Üsküdar(there is a restaurant which is very expensive)u can go there from Ortakoy(very nice town with the Bosphorus' view),Kadikoy could be nice(Barlar Sokagi in Turkish-a street with pubs and street shops which sells some ethnic accessories very close to centre of Kadikoy).And try to taste traditional foods likes kebabs(there r 3932844kinds),lahmacun etc.as a drink try 'raki'.its strong and tastes like greek's uzo.last thing Beyoglu(Taksim) and sultanahmet r a little expensive but still cheaper then other european cities,try to higgle with sellers.thats it 4 now,hope im not so late and somehow u read these before u get istanbul and hope hav a wonderful time in İstanbul.Enjoy it!