Toy roadway
These are the basic parts of a toy roadway for a child to play with. It's a really simple design, and it prints well. Nothing complicated about the printing. My son loves this and it's easy for him to link together. It's also useful for tuning temp, speed, 1st layer, infill, resolution, etc.
Don't forget, you can usually flip the direction of parts in your slicer, so can make the junction and curves fit your needs.