Tours leave from the old harbour and start by taking in part of the city walls, round to the bay by Pile Gate
The boats then cross the open water to the edge of Lokrum Island where they then slowly go round the edge of the island facing Dubrovnik
Using the glass bottom in the boat you can observe the bottom of the sea, along with the Marine life. The water here is crystal clear and teaming with life
The only downside is that there is no commentary or explanations in any language