Jamboreen is a grand carnival held every year on the longest day of the year (the summer solstice). On this day the Eens dress in colorful costumes, wear masks or painted faces, and walk on long stilts while juggling glowing balls or performing other tricks. They prepare treats such as Eenberry pie, honey trifles, and roasted acorns glazed with Een sugar. They sing silly songs, dance to jubilant music, and play such Een instruments as the narfoo, the womboe, the fizzdiddle, and the flumpet. For most Eens, the best part of Jamboreen are the games:

Sneeze Race
Participants wear wheel-skates and try to sneeze their way across a finish line.

Pickle Toss
Two partners throw a slippery pickle back and forth as many times as possible.

Boot Bang
Particpants swing as high as they can on a swing while trying to kick off their shoes, aiming for a long trumpet. If they succeed in getting the shoe down the trumpet, it spins down a long network of tubes, setting off a series of gears and switches until at last a melon ends up dropping—and exploding—on some hapless Een’s head.  

Sink the Boat
This involves cramming as many Eens as possible into a boat to see how many can fit in before it sinks

Ticklefish
Eens try to keep their feet in a tub filled with Een fish as long as possible without breaking into laughter.

Snore War
A game to see who has the loudest snore—though it's usually impossible to award a winner, since everyone is asleep.

The highlight of the entire festival is the Magicians' Match. This is a friendly duel between seven magic-makers. Famous participants in the Magian’s Match have included Gregor Griffinskitch, Kayla Kandlestar, Burdock Brown, and Roompa Ringtail.