The Dying Animal by Philip Roth — not about Zutphen, but the Dutch translation is how A.F.Th. van der Heijden, Zutphen's most celebrated literary son, first encountered Roth's prose and credits him as an influence. Reading either writer gives a sense of the moral seriousness that Dutch literary culture at its best produces.
De Tandeloze Tijd (The Toothless Time) by A.F.Th. van der Heijden — a vast, obsessive cycle of novels following a young man from the Netherlands through decades of the 20th century. Van der Heijden was born in Zutphen and some of the Achterhoek landscape and urban texture of the Netherlands of the 1960s and 70s is woven through the work. Untranslated into English, but if you read Dutch this is essential preparation.
A Bridge Too Far by Cornelius Ryan — the definitive account of Operation Market Garden (1944), the Allied airborne assault on Arnhem and the bridges at Nijmegen. Zutphen is in the same region and the Battle of Zutphen has its own long history; Ryan's book provides the 20th-century context for the Dutch Gelderland landscape you are walking through.
The Embarrassment of Riches by Simon Schama — a sweeping cultural history of the Dutch Golden Age, examining how the Republic understood its own prosperity, virtue, and identity. The Hanseatic wealth visible in Zutphen's buildings belongs to an earlier commercial tradition, but Schama's portrait of Dutch civic culture helps explain why a town of this size thought it worth building like this.