Is this an unused sump pit now covered..

[Mario A. Kyriacou, CHI]

...or something else?
I found this under a floor mat in the basement.

[Vince Santos]

It sort of looks like an old sump pit but not completely round like the ones I see. Plus is looks like there is wood in the corner?

[Mario A. Kyriacou, CHI]

I agree, that is an odd shape Vince.
I believe the wood at the right radius was used for a cover support.
BTW This house is appx. 80 years.

[Nick Gromicko]

80 years old!? It might be a closed-up man-hole cover to an old water or sewer main. Is this home very near a large town?

[James H. Bushart]

You may have found Jimmy Hoffa.

[Nick Gromicko]

Back in Phoenixville, PA a fella sledge hammered bricks (like the ones in your pic) and ended up falling into the 100 year old main water line. In the past, when they built a home over top of an old man-hole cover, they'd seal it up with bricks. The bricks in your pic look old.

[Mario A. Kyriacou, CHI]

You could be right Nick.

[Keith R. Braun]

I routinely see houses older than this and many times this same floor footprint has been filled with concrete. Old coal & oil fired heating units were sometimes recessed into the floor.

[Mario A. Kyriacou, CHI]

Thanks Keith, do you have any photos?

[Bryce W. Jeffrey]

I found an abandoned cistern once. Does it sound hollow when you tap on it?

[Mario A. Kyriacou, CHI]

Originally Posted by bjeffrey

I found an abandoned cistern once. Does it sound hollow when you tap on it?

Yes it does Bryce.

[Marcel Gratton]

Did you scan the area with your IR camera for clues...