KEI-Time Traveller is a kind of virtual time machine that merely requires the use of commercially available GPS phones. In reality, KEI-Time Traveller shows graphical images of a virtual past scene within a given area as viewed from the current location and with arbitrary viewing angles. Users can virtually explore the past world using this system. We applied it to junior high school students, twice. They virtually visited a world of 1938, when a severe landslide disaster occurred, but the designs of interaction with the virtual past world differed between the two fieldwork trials. By comparing the results, we discuss the design of the interaction and its effects on the fieldwork.