Most of my dreams are just exploring sprawling impossible indoor structures, rooms that exit into themselves, overlapping hallways, endlessly repetitive architectures, etc. Most of these also happen to be (in the context of the dream) places that I used to spend a lot of time in, like old houses or schools. Buildings inexplicably becoming other buildings after passing some sort of threshold like a doorway or a flight of stairs or something.
One of my nightmares even had me getting lost in my old high school, which in the dream had become a sprawling multi leveled well-kept urban maze resembling a shopping mall more than anything else, except with classrooms instead of stores. It was a nightmare because I was late for class and I was a huge nerd at the time who cared a lot about things like having perfect attendance.
The first nightmare I ever remember having was discovering a goose in my laundry room. I approached the goose to pet it and it opened its beak, and another beak came out xenomorph style and bit my hand. This was the most terrifying thing I had ever experienced in my young life (I think I was maybe four or five years old at the time) and it left me scared of geese for years after.
I always have found dreams fascinating, and tried to practice lucid dreaming (being aware of and controlling the dream as you dream it) for one summer in high school. Strangely vivid memories of laying in bed sweating in my underwear because of the summer heat waiting and trying to pay attention to my body and mind as it falls asleep. I can recall with almost complete clarity the patterns of colors you can sometimes see when you close your eyes. I took to calling those patterns "invisible colors". Never called them that to any other person because I never spoke about my fascination with dreams so it never came up, but that was just how I referred to them internally. I've only had two lucid dreams that I can recall. The first was very, very short. I dreamt about my garage door. It was shut so I opened the door up. I turned around away from it, and when I looked back it was shut again. This unbelievable turn of fate triggered the realization in my head that I was indeed dreaming, I became elated, I felt a profound excitement and I took several steps and tripped, and hit my head on a nearby parked car and immediately woke up.
The only other lucid dream I can recall having was me being in a school bus. The bus was parked so I climbed out of the hatch in the ceiling on to the roof of the bus. The bus was in the middle of the ocean, perhaps floating or parked on top. I'm not sure but it was surrounded by water. In the distance rising from the horizon was an absolutely astoundingly huge structure, nearly blocking out the sky. It had many, many moving pieces to it, gears and pistons and vacuum tubes. it resembled one of those animated gifs of like a factory with conveyor belts that move colorful balls around and drop them into hoppers or whatever and there's all these different pieces all working to the same rhythm. It was petty much just one of those gifs but unimaginably huge and rising above the landscape like how a cereal mascot rises above the bowl of sugary cereal on the package. Anyways this was too unreal for me to believe in so I realized that I must be dreaming. I distinctly remember thinking the phrase "come on, brain, you've got to be kidding me". So I decided to walk on water, I jumped of the top of the bus and started walking across the ocean, each footstep I took rung out like a crystal bell and a square tile shape around my foot would momentarily light up. I don't remember much else about the dream, eventually I ended up in a department store with my friends but that part is vague and I don't recall it at all other than the most vague ideas.