The game takes place in Volcanica, a place populated by Crunchlings at the center of the Earth. The city's mines have been infiltrated by thieves looking to steal all the crunchium, which is needed to produce Cap'n Crunch cereals. Cap'n Crunch attempts to remedy the situation by having a crunchling challenge the thieves to an athletic competition. The crunchling trains for the challenge by practicing three games, each teaching a different skill.
Speed practice takes place in Backwardia, where everything is backwards. The crunchling races on a skateboard against a turtle to the finish line while collecting pieces of cereal and jumping over obstacles along the way for extra skill points.
Jumping practice takes place in Computica, a place completely made from computer parts. The crunchling jumps up a tall shaft on top of floating memory chips, collecting pieces of Cap'n Crunch and crunch berries throughout the level for extra skill points.
Strength/throwing practice takes place in Jurassica, a dinosaur-filled place in a time when the crunchasaurus ruled the earth. The crunchling has one minute to move back and forth throwing rocks in the air to hit volcanic rocks and pterosaurs flying overhead. Rocks are worth 1 point, while pterosaurs are worth 3.
The player starts by customizing the crunchling's appearance and name. The hub of the game is the crunchling's house in Crunchium City. The player can pet and feed the crunchling three kinds of Cap'n Crunch cereal to keep its happiness and food levels up. The three events that can be practiced are in the corner, with progress bars displaying the level of proficiency the crunchling is in each event. At any point in the game, the player can click the 'Go Online' button and load their crunchling to the Cap'n Crunch website to share with other players. As the crunchling practices each event, it becomes better at subsequent tries at that event. Once they've become good enough at each event, the crunchling will grow. There are three stages of growth in total. After the crunchling is fully grown, it can compete against the Crunchium thief. The Crunchium Thief challenge consists of a single event randomly chosen from the three training arenas. The crunchling will either have to race against him in the speed or jumping games, or out score him in the throwing game.
Cap'n Crunch's Crunchling Adventure was part of Quaker Oats' "Where's the Cap'n" promotion in 1999. The game came packaged as a CD-ROM with double boxes of Cap'n Crunch cereal, or could be ordered by mail with the purchase of a single box. A press release given by Quaker Oats set the retail value at $30. The game revealed the location of where the Cap'n had been and continued his adventures there. The CD-ROM could also be played in an audio CD player, where Cap'n Crunch gives a 20 minute narration of the story in the game.