The "O" or, affectionately and perhaps accurately, the "Dirty O" is Pittsburgh hot dog tradition.  It's a big menu, but the thing to get is their hot dog or a chili dog.  And fries.  Fresh cut fries, fried twice.  Great fries.  That's a small portion above, a mountain of fries that even I couldn't finish.  Order your dogs and drinks up front, the fries at the rear counter.