Lamar-Dixon in Gonzales puts you slightly below Port Allen and the beginning of the plantation tours. Outlet malls and Cabela next to Lamar-Dixon. There is a small park in Convent that will put you almost in the middle of the plantation routes. Plantations are on both sides of the river.
If you stay in Gonzales go to Sammi's at corner of Jefferson and Hwy 61 at Praireiville. Excellent Muffaletas and seafood. Also Mike Anderson's at the hotel-sorry can't remember the name-on Burnside/Hwy 30 south of I-10. I love the stuffed shrimp with crab meat. Ralph and Kacoo's in Baton Rouge. I lived in Gonzales for 30 years and the food-especially seafood-is as good as you will find in N.O..
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