Variant Names Seyh Zafir Türbesi ve Kütüphanesi / Zafir Tomb and Library. As you are going to Conrad Hotel from the Barbaros boulevard in Besiktas District on your left is the tomb of Seyh Muhammed Zafiri from Tunisia. It's Architect & Planner is Raimondo Tommaso D'Aronco Dated to 1904. By some it may even be considered as Art Nouveau--when considering the time period for Turkey this would be quite possible. However, we could also consider the origins of Art-deco in architecture where it is dated to the inner war years of 1920s and 1930s, but some stretch it back to 1900s. This tomb however strongly suggests the latter.
I would call this complex and the fountain near it an Oriental exercise in Art-decorative architecture in Istanbul. Enjoy