Hello Espeland, Welcome to the forums. When "work" is used to mean "the place that you work," you use it without an article. I have to go work now.
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I can't think of how you would ever use the article "a" before "work."
a work is an artistic work, or possibly scientific.
Mahler's Eighth Symphony is a work of great breadth and depth, not to mention length.
Your Chicken Piccata is so beautifully presented that it's almost a work of art.
Einstein's General Theory of Relativit