We spent a four-day weekend in Istanbul, and found The Other Tour by Googling for unusual experiences in Istanbul, and The Other Tour definitely fulfilled its promises. Without giving away too much, we were immersed in the local culture, and got to see parts of Istanbul that tourists rarely see, both rich and poor. Trevor was our guide, providing a wealth of knowledge as well as being a fountain of energy :) It is an experience for the curious traveller, who is looking to see beyond the regular attractions, and not just another sightseeing trip. Do read their websites, and judge for yourself if this is for you.
All in all, I highly recommend The Other Tour if you're openminded, looking for something unusual, and prepared for anything!