Muntz traveled the world in this airship, and has used it to collect various things he found along the way. The giant airship has several chambers, including a dining room, a hall of animal skeletons, and the bridge. The bones of a large bird (the species Kevin is) can also be seen in the airship, including all the helmets of fallen adventurers he has knocked off and stored inside. The airship also has a hangar to carry small biplanes.
During Carl's mission to rescue Kevin, most of the animal skeletons and antiques in the exhibition hall were destroyed and lost (some due to Muntz's violent rage to kill Carl, others due to Dug accidentally pushing the lever that turned the dirigible sideways after being cornered by the dog pack). A small portion of the exhibition hall (the window where some portions of animal skeletons fell on) was also damaged.
After Muntz's death, the airship is now owned by Carl and Russell, with Dug as the new leader of the dog pack.
In the short "George and A.J.", Carl lands the Spirit of Adventure on George and A.J.'s van, crushing it completely, much to their horror.
The Spirit's design is based largely on the German airship LZ 127 Graf Zeppelin, but with 8 engines on her hull that can be pivoted forwards and backwards, similar to the USS Macon's vectored thrust engines.
The airship's aircraft carrying hull is based on those of the ZRS airships used by the US Navy, the USS Akron and USS Macon, and the large hooks on the upper wings of the biplanes it launched suggest similar hangar incorporation to these two ships.
It could also be said that the airship are based on one of Goodyear-Zeppelin's later concept designs, the ZRCV, which was to have an elongated gondola as with the Spirit.
The Spirit of Adventure is described during the news reel shown at the start of Up as "longer than 22 prohibition paddy wagons." The average police wagon of the prohibition era was approximately 25 feet long, making the Spirit's length greater than 550 feet with a possible hull diameter (width) of about 100 feet.
The blimp as seen from the newsreel
Muntz's personal room and dining hall from the newsreel
The blimp as seen 70 years later
The exhibition hall containing Muntz's collection of antiques and animal skeletons
Muntz's personal room and dining hall as seen 70 years later (Note: it now holds his personal research on finding Kevin and his collection of the pilot headgears from previous visitors whom he killed)
The storage room (also the entrance to the blimp) where Muntz held Russell and had him thrown out