When I was six, I was taken to something called a circus for the first time.
Literal
I [topic-は] 6-years-old [attributive-の] time first [called-という] thing [to-に] take-[have-done-てもらった].
サーカスというもの ('a thing called a circus') uses という + もの to mark the concept as unfamiliar or newly encountered — a 6-year-old encountering a new concept. 連れていってもらう ('be taken along') combines 連れていく (take along) with the ~てもらう benefactive. サーカス is a katakana English loanword.