for the fun of itexprexpression: Prepositional phrase, adverbial phrase, or other phrase or expression--for example, "behind the times," "on your own."
(purely for enjoyment)
为了取乐 wèi le qǔ lè
为了开心 wèi le kāi xīn
好玩 hǎo wán
They love taking a drive in the country just for the fun of it.