It took 140seconds to do the import and after the import I now had a new scene called dsntTreasureBookShaft with a single object on it called WatsonJournalCover;
Please look again after importing the descent, and after importing it choose the scene called dsntreasurebookshaft on the pulldown menu upside of your screen.
now zoom out very, very far with the "minus "key of your numeric keypad.
The descent is placed far from center of the "world" so you won't see it at first!
suddenly it appears but very small, zoom it in again while keeping it in view.
In the outliner window you can see the watsonbook in the scenery called "scene" which is the wrong one.
Click in the outliner window on the scene called dsntreaurebookshaft and a whole list opens with all the objects.
Click on one of those objects to activate it.
Place your mouse cursur in any 3d window.
click on the forward slash of your numeric keypad.
this takes the object locally and zoomed in!.
It is a toggle type of switch , when you toggle again your are back into your scenery and you can choose any other object or group of objects.
I am afraid you did just not look far enough, i expect this will help.