"Fun" is a too short termed word i think... "happieness" would perhaps be better:

Riding a sailboat hard on the wind, watching the foam of the waves splatter onto the deck...

Reading a book in a comfy chair, only accompanied by the sounds of a fire...

Learning something new that changes your worldview completely...

Cooking together with your partner...

Watching your children grow...

"Fun"... "fun" is short lived like the buzz you get from a glass of good whiskey, i would say its better to strive for happieness