From Dragon Mania Legends Wiki
“This Ancient Portal leads to the Outer Isles, a land of battles to win and treasures to claim.”
The Ancient Portal is used to travel from the Archipelago to the Campaign Map by selecting it and pressing the button. The level of the Portal determines the base number of Battle Energy available for use on the Campaign Map. Each time the Portal is upgraded , both the Portal Energy and the Arena Energy are replenished. The level of the Portal does not affect the 'base' amount of Arena Energy, as that amount is only affected by the Trainer's VIP Status. The size of the Portal is 7x7 squares, regardless of its level, which makes it the largest movable building in the game.
Trainers of VIP Level 11 and above can switch between the normal aspect of the Portal and a golden variant . The Golden Ancient Portal serves no extra purpose other than an aesthetic enhancement. This option can be used even when the VIP Status is not active.