An alien underground city?!
This was something beyond imagination!
Guang Zhen was first shocked when he saw this, and the thought of what Blue 6 said cropped up in his mind. The legend about cursed planets and how they were life-preserving planets who avoided the attack from a neutron star fragment.
When sentient lifeforms appear on a life-preserving planet, with the natural advancement of technology, they eventually venture into space as long as the race does not face extinction through lack of materials or infighting.
When this race manages to colonize every corner of its solar system, they will naturally wish to venture out of the confines of its own solar system. When that happens, the race becomes a level 2 space civilization.