What could a tourist do/visit on sundays (Istanbul)

Hi there,

I'll be between you in Istanbul next saturday and I did planned nothing to do on sunday.

So in your opinion, what could a tourist like me do/visit on sundays? I noticed that most of museums are closed and I don't want to spend it in my apart and lose time for nothing.

Your suggestions are more than welcome :)

Thanks a lot!
Ps: I have 2 sundays I have to plan things on :ss