公園で遊ぶのはおもしろかった。

(public) park

indicates location of action; at; in; indicates time of action; indicates means of action; cause of effect; by; and then; so; indicates continuing action; indicates certainty, emphasis, etc.

to play; to enjoy oneself; to have a good time; to mess about (with alcohol, gambling, philandery, etc.); to be idle; to do nothing; to be unused; to go to (for pleasure or for study); to intentionally throw a ball to lower the batter's concentration

indicates possessive; nominalizes verbs and adjectives; substitutes for "ga" in subordinate phrases; (at sentence-end, falling tone) indicates a confident conclusion; (at sentence-end) indicates emotional emphasis; (at sentence-end, rising tone) indicates question

topic marker particle; indicates contrast with another option (stated or unstated); adds emphasis

interesting; amusing