What makes a museum?

I love walking through an amazing museum and walking out with more than I walked in with. The thrill of discovery & wonder propel me to go again and again in city after city I travel. Some disappoint, yet most enthrall me with the unexpected & utterly wonderful. I have some thoughts on what makes a great museum that I would like to execute on, but I want to know what you think.

What makes a great museum? Is it the building? Is it the architect? Is it the curator? Is it the exhibits? Is it the gift shop? Is it the cafe? Is it just the whole experience? Is it having specific items or artist on display? What is it that draws you into a museum and hooks you? Is it interactive displays & exhibits? Could it be the crazy and absurd? Whatever it is, I want to know.