RingworldPierson's puppeteers, strange, three legged, two headed aliens, have discovered an immense structure in a hitherto unexplored part of the universe. Frightened of meeting the builders of such a structure, the puppeteers set about assembling a team consisting of two humans, a puppeteer, and a kzin, an alien not unlike an eight foot tall, red furred cat, to explore it. The artefact is a vast circular ribbon of matter, some 180 million miles across, with