How do you entertain yourself at work?

What are some good ways to entertain yourself at work when you don't have enough tasks to do?

• I'm at work and I'm constantly not assigned enough to do.  It would be better if I didn't surf the Internet all day or otherwise bring attention to the fact that I have nothing to do.  Considering that what are some ways that I can entertain myself that won't draw too much attention to me?

• Answer:

  I read about the stuff I love obviously not news and gossip, learning currently a  language so read stuff in that language to improve my language skill, observe other collegues and try to understand what are good things in them that I can learn sit and figure out what should I do next in life. reflect on work/life. anything that train my thinking muscles.