Mailly-le-Château is not on a main railway line and is best reached by car or as part of a canal journey.
By car is the most practical option. From Paris take the A6 motorway south to Auxerre (exit 21), then the D951 south along the Yonne valley. The drive from Paris takes around two hours. From Auxerre the village is about 25 km south.
By train to Auxerre (served by direct TGV from Paris-Bercy, roughly 1h40). From Auxerre there is no direct public transport to Mailly-le-Château; a taxi from Auxerre station costs around €35 and takes 30 minutes.
By canal boat is how many visitors arrive. The Canal du Nivernais runs directly past the village, and hire boats are available from Auxerre, Châtel-Censoir, and Clamecy. The village has a small halte nautique with moorings below the cliff.
By bicycle along the canal towpath from Auxerre takes around two hours on a flat, well-surfaced path — a very pleasant approach in fair weather.