The Dimension cube is a powerful artifact that Enik gave to Rick Marshall when he became the guardian of the Land of the Lost. The Dimension cube has the power to travel between realities and alternate dimensions. Rick used it first to send his children Holly and Will Marshall home to earth. Holly, though apparently found a way to return to the Land when she is older.
Rick was able to use the cube to explore the land of the lost, to travel between the land and earth and many other dimensions.