This is my first time 〇〇ing. I'd like to take a picture to remember this day.
この場合、次のような言い方ができますよ。
ーThis is my first time taking a train in another country. I'd like to take a picture to remember this day.
「海外で初めて電車に乗るので、この日の記念写真を撮りたい」
「初めて〇〇する」は英語で This is my first time 〇〇ing. のように言います。
to take a picture to remember ...で「記念写真を撮る」
ご参考まで!