Yobuko Morning Market fills a short street in the fishing town north of Karatsu, with stalls selling dried fish, vegetables, snacks, and the squid that made Yobuko famous. It is modest, but it gives the coast a working flavour that the central castle area cannot.
Go early, then stay for a squid lunch or continue toward Nanatsugama and Nagoya Castle Ruins. Without that wider loop, the market alone is a small stop.