u/pas_la_mer_a_boire

So, we were doing some renovation work on our annex, found a manhole cover under the kitchen floor, cracked it open and found this. It's about 7 metres down to the water and 1.5-2 metres wide as far as I can judge. The annex was built in 1993. Construction looks solid, the well walls look OK to my untrained eye. I don't really know what do - close it up and move on, get a surveyor in to check it over, report it to local authorities (this is in the UK) or what. It's a bit unnerving, and wondering if anyone has come across this kind of thing before.