Dimensional Tunnels are passages to other worlds, such as the Warp of Confusion. The insides of these tunnels are twisted spaces filled with abnormalities, like plants with spiked balls on them, eyeballs, geometric shapes and random objects like giant skeleton keys, mannequin legs and do-not-litter signs. A road between the entrances into the Dimensional Tunnel also exist here.
In the present day, Sonic found a Dimensional Tunnel hidden inside a trashcan while following the trail of his missing friend Tails, who had been kidnapped by Dr. Warpnik and taken to the Warp of Confusion, and eventually ended up in the Warp of Confusion himself. That same tunnel was used by Dr. Robotnik and his henchbots when they followed Sonic to the Warp of Confusion. When the Warp of Confusion then began to go supernova, Sonic and Tails used the Diemnsional Tunnel to escape back to Mobius, which they managed just in time before the Dimensional Tunnel got destroyed.