What kind of activities make you truly happy? Do you derive the most pleasure from extremely challenging, or extremely easy tasks? Or from activities that you have control over, versus those that you cannot control?
It turns out that there is a state called 'flow', when your skill level (which gives you control) and the challenge of the task complements each other optimally, giving you a feeling of ecstasy as you progress through the activity. At such a high level of enjoyment, time also loses its significance (there is no sense of time passing, or stress of time constraint).
This concept is applicable to all aspects of life -- work, fun, human interactions.
Mihaly Csikszentmihalyi describes the meaning of flow nicely in the following TED talk.
You can aim to achieve a state of flow in what you do, to derive the most pleasure from it. For me, I reach a state of flow when I bake, dance, play the piano, make presentations about my work, and write on this blog. =) Of course, the state of flow is not always attained quickly, as you will need to build up skill and experience at the task to be proficient enough to enjoy the challenge. For example, I learnt dancing and the piano for >10 years, hence it is natural to me now. It also took me 2 years of graduate school to really enjoy making presentations. On the other hand, if your skill is too high, boredom can set in. In that case, try to look for a more challenging version of the task to tackle (such as learning a new piano piece, a new recipe, or increasing the quality of your work).
Where does your flow lie?