Lonely Planet review for Mint
The stately Mint building (1816) was originally the southern wing of the infamous Rum Hospital, built by two Sydney merchants in return for a monopoly on the rum trade (Sydney’s currency in those days). It became a branch of the Royal Mint in 1854, the first outside England.
It’s now head office for the Historic Houses Trust, with a small historical collection and an upstairs cafe. There's not a whole lot to see or do, but it's a worthwhile diversion nonetheless.