The Evangelical Church of Sts. Simon and Judas Thaddäus in Bad Sassendorf is a three-nave, two-bay hall church with a straight chancel built from local green sandstone. As the successor to a baptistery built in 1313, the church was probably built between 1420 and 1500 in the Gothic style, making it an important section of medieval church buildings in the Soest Börde. The listed building features architecture that is characterized by its historical details.
The interior of the church, characterized by round pillars, tracery windows and cross vaults that were only added in 1905, creates a bright and spacious atmosphere. The furnishings include baroque stalls with closed rows of pews, a pulpit and an altar in its original form. Figures of apostles in the choir refer to the origins of the church. The octagonal stone baptismal font, unearthed in 1937 and presumably from the previous chapel, is considered to be the oldest piece of equipment in the church. The dominant olive-green hue of the Soest green sandstone contributes significantly to the defining atmosphere of the room.