That's an interesting view! Frobbin hood said earlier that there was a possibilty to fall through from this museum vent. From your description it probably seems to be the same vent. I did a quick search earlier there but didn't find anything out of ordinary. Apparently, have to check it again. Just to be sure, is it the the vent where you can get high up to those cross wooden beams, above the museum's main display room?