A bit off-topic, this reminded me about the sewer connections between east and west Berlin, which apparently were shared in places but had grates installed to p

A bit off-topic, this reminded me about the sewer connections between east and west Berlin, which apparently were shared in places but had grates installed to prevent people escaping from the east. They also had a subway which iirc served the west but went through a couple of east berlin stations without stopping because the route predated the split.