The Volcanic Titan's kingdom was surrounded by several barriers and arrays to protect it from foreign invaders. The first barrier was the massive mountains forming the crater's outer walls, and the second barrier was the lava pool itself.
There was also the lava Bloop, the ancient guardian monster that lived in the lava. He was the third barrier, and the fourth barrier was a deadly wave of searing heat that was powerful enough to vaporize flesh and bones.
If someone managed to scale the mountains with a large and strong enough ship to sail the lava pool, then somehow managed to bypass the lava bloop and endure the waves of deadly heat, they'd be faced with the fifth barrier.
