When you enter the museum after completing the Underground Tour, you apply for the job and are there the rest of the day. When you leave, it is night and you have to protect the painting from being stolen. Get the remaining dragon picture pieces and go to the Docks to access the Underground.
(see related questions)
get it at night
Counterfeit Island
Night
you don't. the worker blocks you off.
it is at the museum on the top of the museum at..night.
Its a picture of the "Starry Night" by Vincent Van Gogh
Go through the underground tunnels.
hang from the light above it
Counterfeit IslandNo, Counterfeit Island is real. In fact, it'd be better named as "Art Island".
when it's night, hang on the light above it.
there is no mansion on counterfeit island
You do not die on Counterfeit Island.