The most interesting attraction of Ślesin is the triumphal arch, situated by the road to Sompolno. Called "the Napoleon's Gate", it was erected in 1811 in honor of the French Emperor who passed through Ślesin 4 years earlier. The magnificent structure was meant to greet him again in 1812, after (as was assumed) the victorious Russian campaign. However, unfavorable fate meant that Napoleon never saw it.

The arch consists of a main, semicircular arcade and two lower, side arches meant for pedestrian crossing. The elevations of the arch are decorated with pilaster strips ending with Ionic capitals. At the top of the arch is a figure of a Napoleonic eagle.

The structure of the arch was heavily damaged by an oncoming truck in 1972. It was restored in 1976-77, at the same time changing the communication system around it.