Doofania is the city-state which Dr. Heinz Doofenshmirtz created with help from his assistant, Norm, so he didn't have to live in a place that his brother Roger and his ex-wife wouldn't disturb him. He built it so that it floats on the water on an innertube. Before he built the actual "country," Doofenshmirtz made a plush model because he had a lot of felt handy. It was destroyed when Phineas and Ferb fired their Rainbow-inator. A boat full of fishermen in the harbor saw the rainbow, and one of them was so distracted he cast his line onto the inner tube that Doofania was floating on, sinking it to the bottom of the harbor. Minutes later, Doofenshmirtz and Norm resurfaced, soaking wet. ("Hail Doofania!")
Doofania's buildings take the same shape as Danville's buildings. For example, the Doofenshmirtz Evil Inc. building is also in Doofania most likely as the capital or the country headquarters.
It has its own anthem to go along with it but it cuts off a little short.
In the anthem, Doofenshmirtz states that is "founded on spite".
The whole city-state floats on an innertube.
It remains unknown if Doofania's innertube or felt has been recovered or not from the ocean floor.
The country is for "Me and me" (Doofenshmirtz)
He builds the entire city in one day, much like the Big Ideas that the boys make.
The way Doofania rises in the air and slips under the waters is similar to how the Titanic sunk in 1912 in a similar fashion.