House was built in 1964. Slab is about 3 feet across. enter image description here

  • See diy.stackexchange.com/a/91102/18078 if not in current use (sewer system added between 1964 and now)
    – Ecnerwal
    May 3, 2023 at 15:52
  • 3
    Your town may have a record of this. Or the local "Dig Safe" folks might.
    – keshlam
    May 3, 2023 at 17:18
  • 21
    If you open it, the mole people will emerge. May 4, 2023 at 4:52
  • 1
    While highly unlikely in a residential setting, our church's kitchen has a cover like that for the grease pit.
    – SteveSh
    May 4, 2023 at 12:04
  • 3
    Obviously this is where the Morlocks take the Eloi to their dinner parties. May 4, 2023 at 15:17

2 Answers 2


Most likely access to a septic system, or sewer sump.

Impossible to say for sure without gathering some hefty help and picking it off, or consulting old documents about your house. It covers something and was evidently meant to be findable and removable, but not easily removable (don't want kids falling in whatever it is.)

Or, the mid 1960's being what they were, perhaps there's an old fallout shelter under there ;^)

Standard Warning to not so much as stick your head in to whatever is under there without thorough venting, though you probably would not be so inclined for the most likely case.

If it's an actively used septic system, go ahead and have it pumped out, since that has obviously not been done in your memory.

  • A fallout shelter is possible, but it would need to be easier access.
    – Criggie
    May 4, 2023 at 0:50
  • 5
    Might have been made less easy access when it was considered more of a potential liability than an advantage.
    – Ecnerwal
    May 4, 2023 at 0:52

My guess is its a Concrete Septic/Cistern cover. Try lifting it up, there may be a tank underneath...

  • 2
    If it's about three feet across, it probably weighs around 250 pounds. Lifting it could be a bit of a challenge.
    – Mark
    May 4, 2023 at 2:37
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    @Mark The two lifting points are clearly intended for it to be hoisted mechanically. An enterprising backyard engineer could no doubt rig up something, but the original intention was probably to use a backhoe.
    – Graham
    May 4, 2023 at 8:24
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    2-4 burly septic service persons and a couple of hooks (or long bars) would do it. This sort of thing is specifically intended NOT to be easily moved by one person, with the intent of keeping curious children out.
    – Ecnerwal
    May 4, 2023 at 12:03

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