Powerhouse Museum

This museum is a tribute to human creativity in design and innovation in technology. From the oldest surviving steam engine in the world, to multiple light aircrafts and parts of a space shuttle, to the history of the computer and a celebration of over 300 years of the best in decorative arts and design, and a cinema screen from the 30's showing films—including news reels—of the era, this museum has a mind expanding collection of the best human minds can come up with. It also always has the best in travelling exhibitions and is the kind of place you can either duck into for a quick look though or spend all day picking over the contents of.
This has been my favourite museum for as long as I can remember because there's things to touch and buttons to push that are more interesting and less patronising than what most museums expect children to enjoy (in fact I think my Dad enjoyed—and learned as much from—pressing the buttons as much as I did). This is a place teaching you how things work and empowers you with the knowledge that people came up with technology and design—it was all our idea—how cool is that!

One of the worlds oldest working clocks (it's huge ornate and gilded, you won't miss it) is just inside the foyer and there is a regular presentation about it which is particularly interesting considering it's in the foyer so you don't have to pay the entry fee to enjoy it. You can see all the moving parts and get a good understanding about how clocks came about—getting some perspective about technology which we take for granted always inspires me regarding the human race. Practically the Powerhouse is on the edge of tourist Sydney by Darling Harbour, accessible by the small and overpriced (but still fun) monorail and across the road from one of Sydney's best pie and mash cafes (after Harry's Cafe de Wheels of course).