The long-awaited post that was conceived before the ski/tire adventure...there is an outdoor recreation spectrum. I'll call it the Bobber-Everest Scale. On one end are car camping and bobber fishing. On the other end ultra-marathoning and mountaineering. In the middle are paddling Class V rapids, rock climbing and long-distance cycling. Cross country skiing in Illinois is closer to bobber fishing. Pretty much, I've only engaged the first half of the spectrum, and really haven't even pushed the midpoint.
Duration is a key factor. A 14-day car camping trip doesn't send the needle closer to the midpoint when all you've done is lift a beer and drive to town for more hot dogs. A single-day event, like a marathon, though, will send you to at least the midpoint, if not further. Five nights of backpacking, though, bring you closer to the Everest side of the continuum versus one night of backpacking in the same place. One of my more memorable recent experiences, hiking Humphreys Peak, was completed in just one morning. Still, that tops the overnight backpacking trip to Forest Glen Preserve in Central Illinois.
One of the main factors in ranking the spectrum is risk. Surfing I put ahead of downhill skiing because drowning scares the crap out of me. On the Everest side, instant-death altitude sickness tops the risks involved in endurance marathons.
Here is a sample of the continuum at minimum levels of activity. Since the intensity ratchets up so much for the last few activities, the midpoint on the activity list is probably much closer to the Everest end.
Cross country skiing