How Many Portals Can There Be?

After walking the halls for what seems like hours, they come to a big room about the size of an arena. What they see in the room is nothing special. Just a big empty area. Zander leads the way out of the room. 

They walk for a few more hours and come to another smaller room. This one has the looks of something like a storage unit but it too is empty. 

Zander puts his hand on the walls and uses [Topography Hand].

(success. The building has been fully mapped out. There are only two levels. The stairs are just up ahead)

Zander has a very pleased look on his face and runs off leaving the girls behind. 

As the girls catch up to Zander, they see him acceding stairs.