Saint-Georges-de-l'Oyapock sits on the river that forms the border with Brazil, facing the town of Oiapoque on the other bank. A bridge links the two, and this is the only road crossing between French Guiana and Brazil — the start of the long BR-156 south through Amapá.
The town is small and hot, with a lively riverfront where pirogues cross to Brazil in a few minutes. Its population is mostly Palikur, Karipuna and other Amerindian peoples, along with Brazilians and Creoles, and Portuguese is as useful as French. Upriver, the Saut Maripa rapids are the local excursion, reached by boat and a short walk.
The road from Cayenne takes about three and a half hours. Check the crossing formalities before you go: the bridge has opened and closed repeatedly since it was built, and requirements on both sides change.