Glory to Rome!
"Let each man pass his days in that wherein his skill is greatest" Propertius Sextus
Now that I've had time to look it up, these are from the FAQ in the rulebook, which alludes to both questions posed:
Mr. Jack Rulebook wrote:
Is it possible to close or open a manhole under a character?
Yes!! The manholes can open and/or close under a character’s feet (in fact, although on the same hex, the character is «next» to the
manhole and it allows or blocks access to the underground sewers depending on its state).
Is it possible to make a character enter or exit the sewers by a manhole on which another character is standing?
Yes!! But stopping on the hex is not allowed, except to make an accusation.
The first shows that a character at an open manhole is actually "next" to it and so could pass by without falling in (even though it is really dark in London at night).
The first and second both show that a character can end their move on an open or closed manhole.