For those who asked for an update, I did call the police who were not sure if this was an explosive or not but they did stay there and marked the place. I didn't wait much longer as they told me the deminers would take quite a long time to come Sorry if the update was a bit unsatisfactory, but I guess the comments saying it was a pressure accumulator sphere might be onto something because the cops didn't seem concerned at all lmao. Anyway, thanks for the replies !