Being there can give one pause, a slight reminder that the safety found in control of surroundings is at present more removed than usual. The trail is all you have connecting you back to that easier world and losing it would be putting yourself at the mercy of a force that humans have mostly conquered yet allow to live on in certain places, one of which you have entered willingly and must now respect.
I tend to be good at spatial thinking and I like being challenged in navigational way, and wilderness is appealing because of the depth of the wild around me, the removal of background sounds of human activity, the real way that nature reveals want she can do if she's left (well, for the most part) devoid of human management.
Yet the salient thing I notice about wilderness is that, no matter how many people I am with, it feels lonely. I feel lonely there, in a way that isn't necessarily bad but is startlingly real, that fades away when I reach marked trails again even if those trails aren't particularly well visited either. It's curious how traversing an area where the only sign of human passing is a narrow area of worn down underbrush feels lonely in comparison with areas of slightly more obviously worn down underbrush that are occasionally marked with a colored blaze or sign. I know that in some ways it's all a farce, as I've only hiked a handful of miles from a paved road and even if the danger of getting lost is real if I'm stupid then I wouldn't have to travel more than twenty miles any direction to encounter civilization again. Still, in the depth of the forest, loneliness.
Perhaps this is an instinct, a reminder that our rise to civilization was in fact a long struggle against the realities of living in nature untamed, or human-as-intensely-social-creature fear of being without the resources provided by a community of my own kind, or something. Perhaps this is a kickback from how I felt here when I was younger, an only child dragged frequently into the woods by parents who sought all those Emersonean ideals while being too young to understand them and wanting only to play with children my own age.
Rock climbing is also about nature: the nature of gravity and the nature of irrational fear. Irrational in the sense that safety gear is rationally in place but instinct to not be in a such a tenuous position as clinging to a rock always remains. Lead rock climbing is taking that safety gear and putting occasionally between you and it the possibility of a ten? fifteen? twenty? foot fall, perhaps more if your skill at setting up safety gear leaves something to be desired.
Rock climbing can be pretty too, the geology can look interesting and the view from the top can be spectacular, but the relationship with nature is a more visceral one. It is about the nature of yourself, and how hard you are willing to fight against instinct to achieve something you want--without wavering in wanting it when things get scary. When I lead climb, every second is a constant battle with myself to keep from giving in and accepting that maybe this isn't something I want bad enough to try until I fail. It is a constant fight against freeze-and-go-nowhere hesitation. Climbing is a pact with yourself, that you will trust your abilities enough to continue to further the challenge until it is complete, despite the fact that you can sometimes (although not always, and not so easily when you're ten feet from your last piece of safety gear) bail out. It is a pact with yourself that you will not sell yourself short and decline to try because of fear or doubt. The world becomes nothing but the problem in front of you, the mix of sediment and minerals at eye level, the movement of hands, feet, muscles flexing in commitment of going forward into a situation that is not at all certain but must be faced.
The feeling at the top of a lead climb is like nothing else on this planet.