The Castles were unknown ancient structures that were around the empty lands. Each Castle has a significance that leads to power. The first two castles would contain books about their histories, translations and other important information. While the third castle keeps an unknown entity orb that contains an unknown power, which the General believed to save the dying Earth from it's exhausted resources.
The episode and structure were hardly shown on the internet, because of the graphics of the animation, that was the time Oscar has developed yet. But some websites have the animation online. The first castle has the first book. Etrius got into the castle with a dragon guarding it. Escaping with the book, a soldier tries to stop the dragon chasing Etrius but was killed. Etrius picked up the weapon and killed the dragon the moment he was close to the truck. Just after, the dragon explodes and Etrius managed to escape by truck.
The second castle of the series, the second castle contains the second book.
During the mission, Etrius armed himself with a blade and several weapons and entered to the castle just to be shut inside by the door. Though with many numbers of the creatures, with the assistance of the chopper he was able to reach the top. As he was about to acquire the second book, he was bitten by one of the creatures in the arm. Getting the book, he was able to escape by the help of the chopper. Once onboard, he lost consciousness.
The Third Castle is believed to be the answer for Doctor Romanov, where the orb was kept according to the first two books that were acquired by Etrius. It was believed to be a fortress against evil, there wasn't much any clear information about the third castle but it is believed that the orb is kept in the center. The orb has an evil spirit which was able to control anyone whoever touches it.
The Third Castle has a large courtyard, an endless hallway, circular stairs rooms and the orb chamber. There were many other places in the Third Castle. Like any other Castles, the Third Castle has creatures guarding the entire place but has muscled creatures, transparent hydras and flying demons. Making the Third Castle a quiet but heavily guarded place. The Orb Chamber does not only contain the orb, but also has glyphs and symbols in every middle part of the walls. Which Doctor Romanov believed that it is a warning about the Orb and the Castle itself once taken.
A dark energy fog is also triggered from the Castle, though the fog creates the appearance of an unknown dragon. Similar to the first Castle, but is bigger yet deadly to encounter.
The General, four elite team members ( Including Etrius, Beecher, Lloyd and Boomer ) and several special forces soldiers as well as Doctor Romanov were at the third Castle to acquire the orb. Upon acquiring the orb, Etrius' mind was reversed and taken by the orb's power, stalling the General in a short time. Knowing the warnings in the walls, Romanov and two soldiers escaped the area before hell goes loose. The chamber was filled with several creatures in the dark ceilings and attack them. Etrius was shot on the head, Lloyd was possessed and a few soldiers were killed in the chamber.
Again, casualties were increased in the bridge's destruction. Separating Boomer and the General in both sides, the General and Beecher rushes towards to the Courtyard where the helicopters were on standby. Only a few choppers were able to leave the area, as only two choppers were hit. One chopper was completely destroyed, the other did not take much damage.