What's that brown sand-castle box structure in the foreground. That's so wrong.
That's the National Arts Centre, one of Lester B. Pearson's projects to commemorate the Canadian centenial in 1967. I agree that it's not one of Ottawa's prettiest buildings and the inside, though nicely decorated, is very dated. The only thing I really like about the NAC is the double-helix DNA sculptures found in all of the stairwells:
The NAC's Southam Hall is actually a pretty nice place to see a show, very intimate. I saw Just For Laughs with Russell Peters a few years ago from the 3rd row from the top and it still seemed like pretty good seats.