This was an unusually vivid dream, almost overwhelmingly so. The nature and the detailed visual content are both fairly normal but I almost never notice sounds, temperature, or smells to such a degree.
Dreamed I was out in the park in my hometown. Just like it was when I did it IRL it was late afternoon and there had been light rain all day, and the water was nearly up to the riverwalk. The normally clear river was muddy brown and choppy, and everything had a sort of grey cast over it, partly because of the recent rain and partly because of the late hour. Some geese were browsing on the riverbank and by the wooded edge of the lake on the other side of the path, and I could hear and see finches, squirrels, ducks, and cardinals flitting around the branches above my head and in the brush by the lake. As I went the path edged downward, until the ground on both sides was partly submerged in the river. The path itself remained dry and I had my good boots on, so I kept going. Soon all resemblance to the real place was gone, and I was walking along a raised wooden boardwalk with leafless trees and patches of thick bramble on either side, all covered over with knee-deep water. The birds and geese were gone, replaced by blackbirds, lizards, and the odd snake whose scales were the same muddy brown as the river. It got darker as I moved along and soon I started to hear insects buzzing around me, and the clean petrichor smell of the riverwalk was replaced with a very earthy mixture of rotten leaves, dirty water, and animal musk. It was still pretty peaceful and I saw nothing wrong with this, and carried on admiring the scenery as the walk's path got more and more convoluted as it started to weave around trees.
Soon the place was dark like twilight, and the trees got thicker and more gnarled. Bramble came right up to the path now, and while I never had to move it aside it obscured the swamp beyond to an increasing degree, until I could see nothing else except for the trunks of the now ancient looking trees for several meters at a time, standing out a darker brown or occasionally edging right up against the walk. I noticed that the temperature had fallen a bit, and I wished I was wearing something more substantial than a t-shirt, hoodie, and jeans. I zipped up the hoodie and carried on, until I came upon a 90 degree corner, my view around it obscured by another thick tree. I looked around it carefully, to find that the path immediately doubled back, around the tree. There, too, the path went a short way only to make a turn around the tree. I looked behind me, and found that the way was blocked off - the railing squaring off the edge like it had always been that way, with no indication it had ever been any other way. The swamp, I noticed, was now completely silent. Casting about I found that I couldn't spot a single living thing other than myself. The sickly sweet swamp smell was now unpleasantly strong. The buzzing returned suddenly, and very loudly, accompanied by a sort of dull rumbling that was only just high enough to be heard. The rumbling got louder and louder until it drowned out even the buzzing, and I realized suddenly that I was very obviously in the beginning of a nightmare. Just like that I was back on the river walk from before, now sunny and warm, sitting on a bench feeding bread crumbs to some extraordinarily friendly geese and mallards.