I have moved into a Grade II listed rural property, and in our patio is a large square pit that for the life of me I cannot identify so I'm hoping someone can help! The hole/pit 90cm square and 30cm deep, it has a concrete bottom with 3 holes in it and the bottom is built in rather than potentially being removable. The wall shown in the picture is our utility room, I cant see anything else nearby that indicates what the hole would be for. There's no smell coming from it and no water visible through the 3 holes, but our house is almost entirely off grid so I wonder if it is related to our septic tank (a good 30ft away) or the old well (about 10ft away) which is no longer used for the house's water supply but would have been at the time of the patio being built.
We had a very difficult purchase and have no chance of contact with the seller who was in the property for 30 years, so any suggestions at all would be much appreciated! We want to cover it with a grate or similar to make it child-safe but want to know what it is beforehand.
Many thanks in advance for any advice.