Which Ice Age film features the characters traveling into a dinosaur world?

Dawn of the Dinosaurs is the Ice Age film featuring a journey into a dinosaur world.

Ice Age: Dawn of the Dinosaurs is the third main film in the franchise. Its story begins when Sid discovers three dinosaur eggs and adopts the hatchlings, prompting their mother to carry Sid into a hidden underground ecosystem. Manny, Ellie, Diego, and their friends enter this world to rescue him.

The underground setting introduces Buck, a one-eyed weasel, and Rudy, a giant dinosaur who has pursued Buck for years. It also expands the series beyond the frozen landscapes that dominate the first two films. The movie was released in 2009 and was the first Ice Age feature presented in stereoscopic 3D.

Dawn of the Dinosaurs is sometimes confused with The Meltdown, which centers on flooding, or Continental Drift, which centers on continental separation and pirates. The dinosaur world is not the ordinary Ice Age landscape; it is a concealed environment beneath the ice.