The typical dwelling in Iron Age northen England around 500BC was the roundhouse. Built entirely of biodegradeable local materials (wood, mud and reeds) it leaves no trace at all apart from the holes in the ground for the supporting posts.
A well-built roundhouse erected on a well-drained site might last for decades providing the roof was re-thatched from time to time. They look like an attractive, cosy place to live, at least until it's time to look for the bathroom.
A fire would be burned in a central hearth, providing heat, light and somewhere to cook. The smoke from the fire could escape through roof vents, but the whole place must have had a pretty smokey atmosphere and smell. This picture of a reconstruction at the Village of Welsh Life in Cardiff says it all!