I don't find that the downtown has a lot to offer anymore without constant spending. If I do go under the city I typically just like to roam the waterfront on a nice day.
Otherwise I find there are far more options for activities in areas like Bayer's lake or Dartmouth Crossing.
I haven't been for a while, but I used to love going to the Putting Edge (glow in the dark / black light Mini putt).
Another thing I find people getting into again is bowling. There are some good choices for bowling whether you're in the North end of Halifax or Lower Sackville. I'm sure there are others I just only know of those two locations off the top of my head.