Well, if the tunnel isn't a natural underground tunnel/river, then it's possible these are marks from a miners pick, or whatever tools they used to make the tunnel. I don't see any map markings though, personally.
I marked on the picture the only spot that looks like it could have been carved by tools to me. The rest looks entirely natural. Take some better pictures around the rest of the area and maybe there is something, who knows. Be carefull in that tunnel..