Bit of a long story:
A big hole in the ground. And when I say big, it was fairly large. We had decided to build a two-storey extension to the side of our house, wide enough for a garage and entrance hall (and bedroom above), with a bit left over for side access. Getting planning permission was easy, but building control wanted to know where the sewer pipe was because the official sewer plans had disappeared.
So the builders got digging, and found a round, rather large, red clay pipe. Which was the sewer pipe. But on clearing away some of the dug-up earth to make it clearer to the officials, they uncovered something else that was red and curved. Just a little more excavation suggested it was a brick dome.
One of the builders, eager to know what was underneath and how deep it was, stood with one foot on the ground and the other on the dome, and hit it with a lump hammer. Eventually there was a thunk when the broken bricks hit the bottom of the hole. But by then, the builder, who was a smart guy, had jumped off the dome as he realised he was potentially standing on top of a lot of nothing.
Further excavation revealed a hole about 8 feet in diameter and about 20 feet deep, which had been very expertly capped with the brick dome. It had quite smooth walls, so had been expertly carved from the deep chalk layer.
It probably wasn’t a well, not just because of the size, but also there was no evidence of it containing water. Best suggestion was that it was an ice-house as the house was originally a farm manager’s house plus a dairy.
It needed a heck of a lot of filling with non-organic matter (truck-loads of broken tile from a local tile factory) and a metre of concrete on top, plus a reinforced concrete raft to build the extension on. Interesting, but expensive.
The best thing was that it obviously became the talk of the neighbourhood, and we got used to groups of people coming up and peering over the mandatory safety barriers to have a look. One was an old lady in her 90s who had always lived in the area, and said she remembered from before the nearby houses were built, and that there had been a dairy there, hence the idea that it was an ice-house.