The "Lost in Danville Dimension" is the dimension where the episode, "Lost in Danville", takes place. Phineas and Ferb were the only ones to see this dimension, which they did through a portal which closed soon as the Phineas, Ferb and Lawrence from that dimension went inside. This dimension, and the one that appeared in Phineas and Ferb The Movie: Across the 2nd Dimension, seem the only dimensions that are parallel versions of the 1st Dimension.