I run as an alternative to using my turbo ...
I find that running on tarmac does my head in, so I end up running (and scrambling about) in the woods, and usually in the dark, which certainly adds a bit of interest.
I 'spose there's an increased risk of injury (over doing it properly), especially as I almost never warm up, and don't own proper 'running' shoes. I often seem to go out seconds after drinking a cup of tea as well, so end up with a sicky feeling pretty much straight off .
I do a loop of about 4km, and that takes me the best part of an hour, but that's mostly making my own way up and down banks/slopes, over streams / fallen trees / through bracken et cetera.
Actually, I hate running, but it's made much better by running in poor conditions - rain, wind, cold and mud definitely make it more entertaining - I'd almost go as far as to say it makes it tolerable. ... but one needs to do something when it's not riding weather (that avoids resorting to the dreaded turbo).