A reader recently wrote that he thought the Takamori Yusui Tunnel was built as a refuge from WWII bombings. It was in fact a failed attempt to create a tunnel from Takamori up the caldera to Yabe. However, if you poke around a bit in mountainous areas near the city such as Tatsudayama and Kimpozan, you can still spot shelters denizens dug in those days to protect themselves from air raids. An example is below. - William