Rosso is a small, flat town and most of it is walkable. The market, the ferry landing, and the town centre are all within easy reach of each other on foot, though the midday heat between March and October makes walking uncomfortable.
Shared taxis cover the short distances around town cheaply. If you are continuing into Senegal after crossing the river, shared taxis and minibuses collect passengers on the Senegalese side and run south to Saint-Louis. Going north into Mauritania, sept-places (shared seven-seat Peugeot taxis) leave from a departure area near the market when full, heading toward Nouakchott.