After something to do on a rainy day? Take your time wandering around the exhibits on display at Galata Mevlevi Museum. There's always an opportunity to learn something new.
You'll be spoiled for sightseeing choice when in Istanbul City Center. Galata Mevlevi Museum is a good place to begin here, but there are plenty of other worthwhile spots to discover. Blue Mosque, Hagia Sophia, and Topkapi Palace are not far from the museum and will fill in your day nicely.