Sultan Ahmet Mosque, known as the Blue Mosque for the blue tiles adorning the walls of its interior, is one of the monuments of Istanbul that has became its symbol. Sultan Ahmet Mosque's six minarets are unique in Istanbul. There are a total of 16 şerefes (balcony- muezzin platfrom) on the mosque's minarets. That probably figure is a reference to the fact that Ahmet I was the 16th sultan in the Ottoman succession.
Google Maps - Sultan Ahmet Mosque

Sultan Ahmet Mosque built by architect Mimar Sedefkar Mehmet Ağa for Ahmet I, between 1609-1616.

You can go Eminönü - Zeytinburnu Tram.
You get off Sultanahmet Station from Tram then you can see which mosque has six minarets.
You can reach from Eminönü or Beyazıt to walk.
İETT Public Buses - Which public buses to way Eminönü
İETT Public Buses - Which public buses to go Beyazıt