Been trying to mix up the workouts lately...do something different and not get stale.  Yesterday after church, I took the mountain bike to one of our rec centers here.  There are two tracks, one for running/walking and one for biking.  They are both 5K.  Made 3 hard rounds on the bike and in between each, I'd get off and jog a half mile.  
Doesn't sound like much but I hadn't done anything like that in quite a while and my legs were hating me the rest of the day and night.  I'm trying to think of more new things to do while I don't have any specific goal in mind.  I've watched a lot of Crossfit recently and am thinking about incorporating some of the things they do.  But, I know full well I'll never get totally involved in Crossfit.  I have no idea how those people aren't all in back and knee braces.  Maybe because they're half my age?  Naaaa...