Frederik Pohl and Jack Williamson collaborated on several novels, and while Pohl's collaborations with Cyril Kornbluth are better remembered, this pair produced some fine, entertaining works. Wall Around a Star is a sequel to Farthest Star, written about a decade earlier. It's not a direct sequel with the same characters, but discusses the exploration of Cuckoo, a Dyson-sphere habitat with many intriguing alien races. The plot isn't too captivating, but it's a fascinating travelogue kind of book, in old-school hard-sf sense-of-wonder style, and the characters are quite interesting. It was fun, but I didn't enjoy it as much as the first one.