I'm thinking about a fishless aquarium subway vent. A project high up on my bucket list. If I built my own home, the air vents would be big enough to walk through, like a small hall way. The air vents wouldn't just be air vents, they would be a fake aquarium, there would be apparent fish tanks with fish swimming in them, but they are just screens, there are no fish or water. The fake aquarium would also reconfigure itself into a small subway with a small train. To access the train you would open cupboard doors in certain areas of the house, the back of the cupboard would be an opening to a tiny station that is 1 by 3 metres, a tiny train that looks like a toy would take you through the air vents to other parts of the house, but the aquarium screens would be switched off so you would feel like you in a subway tunnel. The small subway train wouldn't be a real train, it would be a series of boxes with skateboard wheels screwed to the bottom, they would be dragged along by an electric bike wheel underneath. Each car on the so-called train would be just big enough for one person to sit in it. The train would be powered by metal plates with a direct current flowing through it from one side to the other, about 4 AMps. The metal plates would be screwed to the floor and also steer the train.
There is a lot more detail to my fishless aquarium subway vent thought, it would take hours to explain it all. For example, the micro train stations would have little seats and train progress displays, glossy A2 sized posters of movies would also be on the wall. There are lots of details. Even the way the aquarium shuts off to become a subway has many details.
Keep it simple, I'm thinking nothing.