[*M]ONSTER CANNON wrote: I was mowing my yard yesterday and ran into this:
After downpours this morning, I was able to get inside and this is what I saw:
I don't know how far down it goes, but do know there was no standing water...it went somewhere. 
That's wild. Was grading my yard after I built a garage (yeah, yeah. I should have done that FIRST! Shut up). Anyway, was running the skid steer next to the house and almost lost it in a hole like that. Turns out that it was an old version of a septic tank. The grey water would run into a pit (my house was built in 1909). I was picking up some old and buried flag stone when I found it. Maybe that's it? Filled the sucker with four yards of dirt, and have to keep topping it off every year. Pain in the ass since I have a flagstone walkway on top of it now. Grrr...
Weirdest thing about the whole project, when I was digging the trench to run power to the garage there were several layers of burnt ash. Still haven't figured out where all that was from. Three foot trench and they were all about 10" apart. That and the marbles. I found enough marbles to fill up a mason jar. Cool ones too.