Doctor Eggman's Fortress

Doctor Eggman's Fortress is a location that appeared in Sonic X and its comic series. It was a highly technological fortress and Dr. Eggman's first known base of operations. Following an attack by Sonic the Hedgehog and his friends on the base, a large-scale Chaos Control transported the base to Earth. It served as Eggman's first base of operations on Earth as the doctor plotted to take over the planet until it was destroyed on the President's order.

Description
This structure is mostly a tall blue-colored circular tower with horizontal lines. A yellow, rounded roof stands on top of it with multi-colored lights directly below it and an antenna standing on it. The interior of the base mainly has circular corridors, going through the base's main structure in a spiral. Deep within the base it has a generator room from where it controls the base's main power systems.

New World Saga
On Sonic the Hedgehog's homeworld, Dr. Eggman's Fortress served as the place from where the doctor planned to utilize the energy of the seven Chaos Emeralds he had collected to activate an infinitely powerful machine inside the base while holding Cream and Cheese hostage. However, Sonic began an attack on the fortress and despite the base's robotic defenses that kept repelled him from the base, Sonic was able to bust his way through the base and enter the room where Eggman was. There, a fight ensued between one of Eggman's robots and Sonic, but Sonic got the robot to shoot Eggman's machine with the Chaos Emeralds, causing a massive Chaos Control that warped everyone and the base to Earth through time and space.

The base ended up on a unnamed island in the Southern Sea, where Eggman began planning to conquer Earth. There, the base served as Eggman's first center of operations on Earth, from where he send out several of his robots to aid him in his schemes, but they were every time destroyed by Sonic and his friends.

Eventually, the ongoing warfare with Eggman concerned the President, who considers Eggman a danger to the human society, and resorted to take action and find a solution to destroy the base and put an end to Eggman. The President and his advisors therefore decided to send in two of G.U.N's agents, Topaz and Rouge the Bat, along with a group of soldiers to infiltrate the base and investigate it. Once they got inside the base, the group managed to make a near-complete map of the base. Before they could start looking for the generator room, however, the majority of the group had to retreat as daybreak came, leaving only Rouge and Topaz to look for the generator room. Despite coming under attack by E-70 Noizi, they located the base's generator room and Rouge managed to destroy E-70 Noizi with Topaz's help, before escaping with Topaz.

When Eggman left the base with E-35 Funfun to collect a Chaos Emerald, the military launched a large scale two-pronged assault at the base from both sea and air, with most of their arsenal keeping the base's defenses focused on them, while in secret, sending a special force, led by Rouge and Topaz, to destroy the generator room. Also, due to Dr. Eggman's absence, the operation went slightly easier for the military. Amidst the attack, Knuckles joins with the G.U.N special force to help them locate the generator room. Eventually, they found the generator room and began planting explosives there, but as soon as the explosives were set to count down, they were locked in the generator room.

Meanwhile, Dr. Eggman returned only to witness the attack on the base before reentering it and began attacking Sonic and this friends in the X-Tornado, who had followed him. However, Sonic and his friends avoided the attack and got Sonic into base to find the doctor. Meanwhile, Knuckles and Rouge attempted to bust through the door in order to escape, but with limited success. Eventually, Sonic confronted the doctor in his new robot, E-18 Guerra-Hard. Sonic was initially overwhelmed by Guerra-Hard, but he managed to defeat it and take the two Chaos Emeralds powering. Using the Chaos Emeralds' power, Sonic destroyed Guerra-Hard and tore through the base while freeing Knuckles, Rouge and the G.U.N forces. Eventually, the bombs detonated as well, destroying the base for good while everyone escaped unharmed.

Archie Comics
Doctor Eggman's Fortress also appeared in the Sonic X comic series published by Archie Comics. In this media, it is revealed that the island the fortress is on is located off the Emerald Coast.

Trivia

 * The fortress was incorrectly referred to as "Chaos Control" during its debut in "Chaos Control Freaks" and during the flashback to that episode in Cracking Knuckles. This was either due to a scriptwriting error or the 4Kids Entertainment's producers' lack of knowledge of the Sonic the Hedgehog series.
 * Sonic X #1 also incorrectly referred to the fortress as "Chaos Control" in the first page.
 * The island and its base bear a slight resemblance to the Egg Carrier Island.