This Boulton and Watt engine - the third built - oldest extant steam engine, dating from 1785 and now in the Powerhouse Museum, Sydney.
It built up a head of steam as we got nearer, and then just as we did the wheel began to turn.
More about it here.
Built up a head of steam today myself, when I got to the latest quilt. Just a little more quilting to do and then I can bind it.