beginning serious cross-training

Since I finished taking the GA bar this summer, I have resisted being inside unless forced to (eg b/c of work). However, with the recent time change and shorter days, I no longer can deny that much of my marathon training will (may) be inside. In fact, today I will formally add spin to my marathon schedule (I have done some yoga, etc). Although I enjoy spin, recently, most of my marathon training has been in the Chattahoochee national forest with my dog. Our weekly afternoon schedule is as follows: I leave work promptly at 5pm; I run home; I grab Grendel, put him in the front seat, and we are off. But, today, I will leave work promptly at 5pm and drive to another building to sit on a bike for an hour while being loudly encouraged by an enthusiastic instructor (for which I am grateful, but quasi-resentful because the person is so happy). I know it is inevitable, and on my Hal Higdon intermediate training (http://www.halhigdon.com/marathon/inter1.html), but I was still blindly hoping for more afternoons to watch the leaves fall.