How to get to the top floor of Hall of Heroes

Top floor hall of heroes access (above library):

You gossip, 'how the heck do u get up there'

You gossip, 'i've gotten 2 keys in there and never been able to open the top floor hatch'

Sparton gossips, 'have to get key from christine, go to imm museum, get key from driz and then open the trapdoor on top'