Situated at the end of the Heraklion’s inner harbor near the Old Harbor jetty is the Koules Fortress. Koules is the Turkish name for the fortress but the Venetians dubbed it the Rocco al Mare and the Castello del Molo in the 16th Century. It was a defensive mechanism, which stopped the Turks for 22 years and then became a Turkish prison for Cretan rebels. The harbor is now a drop off point for commercial and passenger ferries; the inner harbor is a concrete maze of apartments that now forms modern Heraklion.
The exterior is impressive, decorated with three stone lions of St. Mark (a symbol of Venetian imperialism), as well as embankments and cannonballs that will transport you to another century. Inside, you can find art exhibitions. Music and theatrical events are held on the upper level. Make sure to make your way to top for impressive views of the harbor. A thorough visit should take about an hour.