What I wanna know is how bad did it smell??? You will find some funky microbes metaboilizing down there! (sorry for the nerd burst of glee at seeing a biofilm laden tunnel early in the am)
It's so bizarre that you found a lemon slice...looked fresh too! I think you guys *just* missed the "Tunnel Lemonade Stand" ....Tunnel Lemonade....hmmm....sounds.........refreshing?!
Thanks for sharing your pics! I like the one with the black.....slime? Bacteria? myxmycota? Weird and bizarre, so, awesome!