On a recent visit (where we had our main tour to Gallipoli booked in advance) we found that the hotel was able to organise other tours at short notice - and as far as I could tell at little price premium.... presumably some kickback was involved but the service was so fast and efficient I'd have been happy to pay extra anyway... haing not been there before that made life much easier...

If you stay in Sultanhamet many of the main attractions are a VERY short walk... (amazingly so IMO )