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に行った時

when (someone) went to

→ に
phrase Uncommon #16,767
when (someone) went to Used after a destination to mean “when [someone] went to [a place].” The past form 行った indicates that the going happened in the past; 行く時 means “when going” or “when someone goes.”
JA: 京都に行った時、古いお寺を見ました。
EN: When I went to Kyoto, I saw an old temple.

その鳥なら、沖縄に行った時に見たわよ。

I saw that bird when I went to Okinawa.