We’ve all heard how rare and precious the Nicholas Building is, but few of us have had cause to go inside. Much less to visit the Salon. This Sunday is Open House at a few of the city’s otherwise hidden treasures. Come Friday, City of Melbourne staff’ll be tidying their desks, as the impressive CH2 building opens its six-green-star rated doors to the public. And things might get a tad packed in the St Paul’s Cathedral bell tower. There’s the chance to see the bits you would never otherwise see of Melbourne Town Hall, the Manchester Unity Building and the Regent, among others.