Geiger–Müller Muon Telescope in Taiwan (GMT$^{2}$) is an education program for undergraduate students to develop a muon tomography detector composed of Geiger-Müller (GM) tubes. GMT$^{2}$ consists of two identical detector plates aligned on an axis at a distance. Each detector plate contains two orthogonal 1-D arrays of 8 GM tubes (L= 18 cm, \o= 2.2 cm), forming an $8\times8$ grid. The arrival direction of muons can be reconstructed by extrapolating the impact points recorded on two detector plates. Field of view (FOV) of GMT$^{2}$ is adjustable by varying the distance between two detector plates. Small size and low unit price of GM tubes make GMT$^{2}$ affordable (USD700) and compact ($40\times40\times40$ cm$^{3}$). Several muon tomography experiments were successfully carried out for buildings, such as C.C. Leung Cosmology Hall, National Taiwan University and Taipei 101. In this paper, we report details of system design, detector construction, data acquisition, data analysis, and results.