The Five Senses realm. The goal of this realm should be obvious just from the name; it is the stage of martial practice where an upcoming martial artist strengthens their five senses as much as they could.
It was commonly believed that the fabled spirit sense could only be acquired upon breaking through to the Foundation Establishment realm and only through immortal cultivation. Still, the martial artists of Tianzi roared in defiance toward this.
Even though one could not birth a true spirit sense after completing this realm, they could have something akin to half of it, able to scan their body and their immediate surroundings but unable to use any of the other miraculous features of spirit sense.
It was precisely because this realm focuses on enhancing the senses that it is likened to Foundation Establishment early. Even then, it was only when one reached the peak of the realm and was ready to breakthrough the Houtian stage.