Marché Dantokpa: People say it's the biggest market in West Africa. Spend an hour or two walking through the labyrinth of stalls and get a sensory overload. You may be inclined to purchase an "Obama girl" T-shirt and matching underwear too.

Pounded yams (igname pile): Benin's best dish. Many places make it. Get it with Wagashi (a cheese) and peanut sauce. Ask around to get recommendations on a good place, or better, invite yourself over for dinner somewhere.

Fondation Zinsou: exhibition centre for contemporary African. Free of charge. 

Bars in Fidjrosse-Center: Fidjrosse (fee-dro-say) is a neighborhood on the western side of Cotonou. There are some great bars right on the beach. 

Yes Papa- if you're there on a friday or saturday, you can listen to great live music (mostly reggae). Drinks are normal prices. 

Best free thing: Benin is one of the friendliest places in the world. Start a conversation with someone and ask to hang out.