That is a deep question.
I think true happiness is the ability to love what you're doing, in the present moment.
Even something as routine as doing the dishes can a happy time, if you savor the experience.
The feel of the hot, soapy water.
The sense of accomplishment in getting something done.
The gratitude for dishes to do and a warm house to do them in.
To me, it's all about being present in what you're doing.