Most of my inspiration comes from every day activity, believe it or not. Adventures, adventure-sites, and even the design of cities is generally compounded from various experiences I have throughout my day. I tend to pay close attention to little things in nature, like what the ground looks like as it cants, or how the stone face of a hill emerges from the soft earth.
I don't know why, but standing out amongst the trees and the rivers in nature inevitably gives me ideas. Even if it is just how to better run a random encounter, I find myself perpetually thinking of things that could go on in that environment: from an attack by orcs (how long would I have till they were upon me? What distance would I be able to see them at) to a raid on a backcountry still that turns out to be more than it seems (a CoC conceit I've been holding in reserve for a long time).
Wilderness encounters are all over the OSR of late, which is strange since I've been meaning to write this particular article for several weeks. Had I followed my own schedule of what to post when, I would have written it around the time of the highest wilderness-encounter hubub due to an idea that had been fomenting since I was in San Francisco. That, of course, is the notion of wilderness encounters, particularly ones that aren't simply violent shake-ups with bands of roving orcs. One of the things the now-defunct Grognard was supposed to provide was a section on encounters with various complex entries that could be added to encounter charts.
I like to incorporate non-combat encounters (or combat-avoidable encounters) in as discreet a manner as possible when describing travel. I have a tendency to describe the entire journey, though I hope not in a way that would be perceived as boring. But because I can throw a lot of little bits of flavorful description in there, it means I can pass potential encounters off unnoticed; what would happen if the PCs stopped to investigate that field they passed on day two, for example? Well, perhaps they would find that it was a druid's meeting ground, or see a newly dug grave, or even a cache of treasure hidden in the earth when its owner decided to flee the region.
These are things that occur to me all the time. So I urge you to keep your eyes out when you're walking or driving around. Any of those momentary flashes of inspiration that come from nature can be added to your games to good effect! Even a question as minor as "How would I describe this terrain feature?" can be at least partially answered by looking at nature around you and contemplating its form. Indeed, every time I see an interesting flower or person or bit of landscape I conjure up several descriptions of it in my head just to stay in practice.
Does that make me a madman?
No. It makes me a DM.