Inside there is a small ornamental castle that is really much larger than it looks inside. Inside the castle is where Cosmo and Wanda usually sleep, although in some episodes they are seen sleeping as goldfish floating in the bowl outside of the castle. The interior of the castle also contains the Hall of Fame and the Hall of Infamy, where godchildren good and bad alike are memorialized. There is a special Hall of Timmy which Cosmo and Wanda have dedicated to Timmy because he is their best godchild ever.
The bowl is round and filled with water, with purple gravel at the bottom. Behind them, there is a castle with many rooms inside. The castle is also where Cosmo, Wanda, and Poof sleep.
Cosmo and Wanda's fishbowl has been the subject of just as much abuse as its occupants. Timmy often brings the fishbowl with him to places a kid normally wouldn't bring them, such as a freezing cold mountain ski range which resulted in the bowl and its occupants being turned into ice cold "fairy god-sicles" until they were thawed out.
- Timmy was the only godchild that went inside the fishbowl.
- In Super Bike, the episode starts with Cosmo and Timmy in a cage that is being lowered into a body of water, at first you think it's the ocean but it really is just the fishbowl.
- Some of the episodes in Season 2 start with a scene in the fishbowl.
- The fishbowl has been in almost every episode.
- In 2004, Nickelodeon released an actual fishbowl based off of it which including the same castle, rocks, and Cosmo and Wanda figures used to decorate. It has since been discontinued.
- The castle has been absent in some episodes as well as some scenes.