I'd definitely recommend a trip of the water bus (or water taxi as it's often called in Cardiff) whether you're from the area or just visiting.
On a sunny day it's a wonderful way to get out of the hustle and bustle of the city and view it from a totally new perspective.
At £4 for a return trip it's not the most economical way to get to the bay but it's one of the most fun. There are other operators that run water buses such as Aquabus (http://www.cardiffaquabus.com ) but I haven't seen much of a difference in them.
If you can, visit the Cardiff Bay Visitor Centre first (free entry) as this will tell you the story behind the mysterious bubbles that you can see dotted on the surface of the water. read more