Japanese Tunnel actually seems to be on the edge of the Davao city. Once you start hitting some of the more hilly area west of the city proper, you'll be coming close to the Japanese Tunnel. It basically is a historical location developed into a tourist spot.  This place not only has the tunnel but also a Japanese restaurant and some rooms to stay overnight in.

The Japanese tunnel was created back in World War II era supposedly by Filipino prisoners of war.  The purpose of the tunnel was to be a hideout not only for soldiers but also their belongings.  It has been said that many tunnels were actually dug back then during or soon after the United States took over Davao City.  

The actual size of the Japanese tunnel seems to be rather small.  Actually it will extend farther than what you will be able to walk.  Apparently, this particular tunnel is owned by two different owners.  The part of the tunnel that you can not go is at the end with bars blocking the other part.

The historical significance of this tunnel made it rather interesting.  The tour guide tthey had at that time really did not give enough information about all the details that would have lent a lot more intrigue into the tour.  Make sure you ask questions if you desire to gather information like that.  You might leave there thinking that the tour guide should be a little more prepared to give a somewhat in-depth history regarding the tunnel but you also might get a different tourguide.

Anyway, if you're interested in World War II history then you'll likely find it interesting even if the tour guide did not seem prepared.  It is recommended that people take a look at it since it only costs 20 pesos per adult.