A preface, or perhaps, a caveat: WI 42 and WI 57 have been slated for (or, really, are endlessly being debated about) widening and straightening for years. South of Sturgeon Bay  the road has already turned into mad swells of multilane madness. Thereafter, the leviathan transportation bureaucracy began eyeing stretches north of town. Grimly efficient, WI 42 north of Sturgeon Bay is approaching interstate whooshing.
WI 42 has perhaps the most intriguing history of any country road. Not your average farm-to-market remnant, it was hewn from a tundralike wilderness in 1857 by starving millers and fishers desperate when winter arrived earlier than expected and froze supply boats out of the harbor.
On the way to Egg Harbor  out of Sturgeon Bay, a great on-the-water side trip is along Highway B. Eventually, it merges with Highway G around Horseshoe Bay and leads directly to Egg Harbor.