Dunno how long you'll be there, but Istanbul is a European City of Culture this year so there will be a lot of events to see (I've seen the brochure).

One good place to find out is the municipal bookshop (Istanbul Belediyesi Kitabevi - blue shopfront) halfway up Istiklal Caddesi in Beyoglu (use the Tunel to get there). Or the Mephisto bookshop/CD shop/cafe at the top of the street.

I'm amazed that people are still repeating that bollocks about train gassings.