I can describe such a tank that is at one of the local fish stores.
It is a marine tank. The rock in the center makes a column as high as the tank and all the plumbing is hidden in the rock. If you look carefully in some of the caves you can see inlet and outlet plumbing, but this was really well done, it is not like the plumbing is very noticeable.
Go to their web site, Aquarium Concepts, in Dublin California, and watch the pictures. Several are of this tank, both close up and from far away. It is a cylinder, about 6' diameter, and over 8' high. I understand it was made larger, but they could not get it through the door, so they had to cut down the height.