I accomplished that goal I had to bike either my age in years (miles) or a metric century (100 kilometers, or just over 62 miles). (I also did that in 2007, looks like.) (I rode 63.5 miles.)
Mostly, I had a really good time.
I saw a skunk. At first, I saw this black bobbing thing with some white, and thought maybe there was a crow with something white in its beak hopping down the bike trail. And then I realized it was a skunk, and stopped, a good 30 feet away. The skunk also stopped, and raised its rear a bit (but was still facing me). I thought, oh, this could be VERY bad.
But then after a short moment, the skunk decided that I wasn't really threatening, but was big enough to be avoided, and it made its way to the side of the trail and into the underbrush. I waited long enough for it to be out of sight, and hopefully out of range of where it would feel threatened, and then bike on by on the far side of the trail. And all was well.
I rode a trail I like not too far from where I live, which starts in a town, and then a couple miles away has a trailhead (where I parked), and then goes about 18 miles to a state park with a circular road, passing through a couple small towns along the way. So I started at the trailhead, rode to the state park, rode around the circular road several times, then back, beyond where I'd parked towards the other bigger town, and then back to where I parked with about 8 more miles to go. I stopped, refreshed my water with icewater from the car, drenched myself with lukewarm water, and then rode the final little bit towards the park and back.
Mostly the ride was fine, but the last 6 or so miles my wrists were really achy.
However, my feet didn't quite fall asleep (I kept doing stretches and stuff along the way which help), so that was a huge positive thing.
I started earlyish, and by the time I was doing the circuit of the state park, campers were starting the morning. And since I did four or five circuits, I saw the development of the morning in several camps. My favorite had a bunch (maybe 12) seats around a campfire. The first circuit, someone was starting the campfire. By the second circuit, it was going well, and there was some movement of other folks around. But the third circuit, all the chairs were full of people eating breakfast. And by the final circuit, all the chairs and the camp seemed empty.
Earlier this summer, I thought about trying to do a century of 100 miles this summer, but now I'm rethinking. It would probably take me 8 or 9 hours (because I'm slow, and would be riding alone), and I think my wrists would really hurt, and I don't think I want to spend that much time on a bike not having fun.
So I think I'll find a different summer goal, maybe something running, which would take less time, but still give me a good goal. And I'll bike and enjoy shorter rides, up to maybe 50 miles, and really focus on the fun of biking, since no one is paying me enough money to have my wrists ache. (They were fine by the next morning, and my legs, while tired that night, were perfectly happy the next morning.)
And I think I'm going to try to go camping at that park for a night. It just looked so beautiful.