Exactly the right question to ask. I was thinking new architecture, refactoring for improved code, ease of adding new features, etc., perhaps in preparation for the next round of features. In that case - the engineers building it! (Not the managers...)

Get a dog - I got a dog because I wanted one, but was amazed at how much more active I was simply caring for the dog - minimum of 3 walks a day, plus playtime.

Take up an active hobby - make sure it is something you enjoy and will stick with. I took up inline skating and just love it. I do it for fun, and the exercise I get is a bonus.