Though it has a lovely medieval center, the small city of Sibenik (pronounced shibenik) is used primarily by cruise lines as a drop-off point for cruisers headed to Krka National Park or other small towns in Croatia. The port is typically found on Dalmatian Coast and Adriatic Sea itineraries. The oldest city in Croatia (actually built by the Croatians as opposed to Greeks or Romans), Sibenik was fortified over the centuries to protect its inhabitants from the Ottoman Empire and many of its medieval fortifications survive to this day, including towers and fortresses. One of the fortresses, the St. Nicholas Fortress, is a UNESCO World Heritage site (but not easily visited), as is the city's medieval cathedral.
But Sibenik also holds a place in modern history. Located not far from where Nikola Tesla was born, the first hydroelectric power plant designed on his theory of alternating current (AC) was located at the nearby waterfalls in Krka National Park, and the city was the first in the world to be lit by street lights powered by AC. (You can see the remains of the original hydroelectric plant during a visit to the national park.)
Sibenik was also marked by more recent history, as a target of the Serbians during the unrest of the 1990s (called the "Homeland War" by people in the region). Parts of the Cathedral of St. James were destroyed by bombings during this period, but it has since been restored; guides will talk about the war if you ask.