The LEGO Ideas River Steamboat (21356) is a 4,090-piece building set designed for adults ages 18 and up. This model recreates a classic river steamboat with functional paddle wheel mechanisms, a detailed steam engine featuring moving pistons, and multiple furnished decks including crew quarters and passenger areas. The design incorporates period-accurate details throughout the structure. When assembled, the model measures 27 inches (69 cm) long, 15.5 inches (40 cm) high, and 5.5 inches (15 cm) wide. The paddle wheel can be activated for interactive play. Builders can use the LEGO Builder App for 3D viewing and progress tracking. This set originated as a fan-designed concept before being produced by LEGO. Once completed, it serves as a display piece highlighting 19th-century riverboat craftsmanship.