The most interesting attraction of Ślesin is the triumphal arch, located on the road to Sompolno. Known as "Napoleon's Gate," it was erected in 1811 to honor the French Emperor, who had passed through Ślesin four years earlier. The grand structure was intended to greet him again in 1812, following what was assumed to be a victorious campaign in Russia. However, fate intervened, and Napoleon never saw the arch.

The arch consists of a main semicircular arcade, flanked by two lower side arches designed for pedestrian passage. The elevations are adorned with pilaster strips, each ending in Ionic capitals. At the top of the arch stands a figure of the Napoleonic eagle.

In 1972, the structure was severely damaged by an oncoming truck. It was restored between 1976 and 1977, during which time the surrounding infrastructure was also modified.