Ground penetrating radar (GPR) and magnetic methods were used at Ghasr-e-Shirin
town in Kermanshah province, southwest of Iran for detecting a series of large ancient
(ca 1500 years) underground cavities (Tagh). The area of study is a historical monument which is named as Emarat e Khosro. Radar and total intensity magnetic field measurements have been done on the eastern part of the complex, where some underground man-made cavities are located. Radar and magnetic profiles indicate these cavities easily. Radargrams, total magnetic map, first horizontal derivative and first vertical derivative of total magnetic field indicate the location of the anomalies, which conform with the real situation. A comparison of results of 50 MHZ and 100 MHZ radargrams shows that the latter distinguishes the anomalies better. This work is completely experimental to indicate the effect of underground cavities on radar and magnetic data. It is concluded that a combination of these methods is a proper tool for delineating underground cavities.