The Iso-Pappila Open-Air Museum, maintained by the municipality of Mäntyharju, is located in the centre of Mäntyharju. It takes its name (“the Big Vicarage”) from the parish vicarage built during the time of Provost A. A. Berner. When completed in 1812, it was the second-largest building in the parish after the church. The current Empire-style appearance of the vicarage mainly dates from 1854, although the building was further extended in 1933.

In addition to the vicarage, the museum includes a servants’ house from the 19th century, as well as a storehouse, a combined woodshed and carriage shed, and a large stone barn built in 1899. The farmyard also features a drying barn, a smithy, several cellars, and a garden.

The servants’ house has been furnished like the living room of a typical local farmhouse. At the other end of the house there is an extensive exhibition presenting the history of Mäntyharju. Among the items on display are photographs taken by the local photographer Nestor Kurvinen and examples of his photographic equipment. On the upper floor of the barn there is a diverse collection of horse-drawn vehicles.

During the summer, the main building of the vicarage hosts exhibitions with various themes, and a museum classroom and a café are also open to visitors. Summer theatre performances are held outside in the museum area, and sheep graze in the nearby meadow.

Art Center Salmela is located close to the museum. Exhibitions in cooperation with Salmela, such as works by the sculptor Nina Terno, are held on the ground floor of the stone barn.

Next to the museum area there is a veterans’ park featuring a soldiers’ dugout, combat and communication trenches, and a World War II artillery piece. In Mäntyharju there are also memorials marking the sites of the first local industrial facility—a sawmill (address: Rantapuisto, Asematie 5)—and the site of the battles of Mouhu in 1918 (address: Mouhuntie 388).