And you can increase the effort some days by adding hills instead of speed.
Yes. There is no shortage of hills in our part of the world. I think I could get a good workout just doing laps of the tiny hill in my backyard.
And it seems much less icky on rainy days than riding a bike.
I was thinking the same thing today. I'm in recovery mode so I could run or bike but the trails are wet and I spent a looooong time cleaning my bike after Saturday's race. So it's going to be a run! (Unless things dry up a lot.)