This study aims to explore the elements of mathematics, especially in the geometry of flat shapes (ethnomathematics) at Candi Lumbung. The method used in this research is descriptive exploration. The data used are data obtained through literature studies, observations, interviews and documentation. Interviews were used to determine the cultural aspects contained in Lumbung Temple. Observations are used to determine the mathematical aspects of Lumbung Temple which is located in Candi, Nngangrukbaru, Tlogo, Kec. Prambanan, Sleman Regency, Yogyakarta Special Region. Documentation in the form of temple photos that contain elements of mathematics and can support the data that has been obtained both interview and observation data. The results of the research are that there are mathematical elements in Lumbung Temple, namely the concepts of rectangles, trapezoids, squares, and triangles which are then associated with fundamental activities that can be used in learning mathematics, namely (1) counting is used to calculate the number of temples consisting of the main temple. and perwara temples, (2) measuring is used to measure the area of the terrace at the temple and the area of the temple, (3) locating is used to determine the cardinal directions and the location of the temple, (4) design is used to find the geometric shape of the temple, and (6) explaining is used to find out the history of Lumbung Temple.