It is a millenium project of the Drumheller Regional Chamber of Development and Tourism
There are 106 stairs inside the dinosaur. The entrance is just behind its right leg. There is a viewing area in the mouth. It is approximately 62 square feet and should hold 8 - 12 people at a time. Fossils and bone are embedded in the walls off the enclosed staircase. The actual height of a real T-Rex is 15 Feet (4.6 Metres) and 40 Feet (12.2 Metres) long.
Construction began November 30, 1999. The monument was built in three pieces (base, body, and head), with the assembly of the three pieces August 17, 2000.
Here are photos of the interior of the dinosaur:

Here are photos of it under construction:

More information about it, and its construction can be found at http://www.dinosaurvalley.com/dino2000/home.html .
Drumheller features many monuments including approximately 32 statues by Trygve Seland :
Dinosaurs of Prehistoric Park |
Dinosaur |
Tyrannosaurus Rex |
Little Church |
Information Source: Dino 2000 Fact Sheet , The Drumheller Mail August 23, 2000 (pages 1 and 3) and August 30, 2000 (page 11), and http://www.dinosaurvalley.com/dino2000/home.html .
Picture Source: Ricky Tsang , and DMY