In recent decades, indoor positioning techniques have been researched to support automatic guidance for visitors in public buildings such as museums, galleries, etc. The exhibition goods nearby could be introduced by a smartphone after the location of the visitor has been acquired. This paper presents an indoor positioning scheme utilizing smartphones equipped with inertial and magnetic sensors. The positioning method could handle complicated human motion and various ways to hold the phone. This is achieved by applying an improved Pedestrian Dead Reckoning (PDR) algorithm and an error-tolerant magnetic map matching algorithm. The improved PDR algorithm estimates walking distances and direction in real time. As long as the user stops to appreciate showpieces, the improved PDR component will report relevant data to magnetic calibration component. Based on the updated information, the final location of the user could be calculated utilizing the relevant data, the real-time data of magnetic field sensor and the magnetic map acquired in advance. We evaluate this method using experimental measurements in practice.