Summary: The Doctor and Rose visit a world where nothing is wasted.
The architecture of the city was unlike anything Rose had ever seen; not exactly ugly, but certainly bizarre. The buildings were made of multicoloured blocks that fitted together a bit like Lego, and the streets appeared to be made from slabs of similar stuff.
“I’ve never seen bricks like that. What are they made of?”
“Trash. This planet doesn’t have much in the way of stone or metal ores, so the people had to learn to innovate. Other planets send their rubbish here. It’s treated, compressed into blocks, and used to make buildings and furniture. It’s very clever. Nothing’s wasted.”