Bowl of Heaven (Gregory Benford and Larry Niven)

Benford and Niven together have upped the ante on Ringworld. A ship carrying passengers in frozen sleep on the long, long voyage to colonize another planet come across a gigantic hemispheric structure traveling on almost the same path, and stop for a visit. They encounter aliens of several varieties and mind-blowing technologies as they struggle to survive and to understand their situation. When I started this book I didn't know it wouldn't be finished in one volume; to find out how things resolve, I will need to read at least one more book. The sense of wonder is strong in this one, but the characterization doesn't live up to the rest of it. Still, worth the read, and I'll read the next book when it's available.