YOU SAID:
先週デパートにかいものにいきました。
INTO JAPANESE
先週デパートにかいものにいきました。
BACK INTO ENGLISH
I went shopping at a department store last week.
INTO JAPANESE
先週デパートに買い物に行きました。
BACK INTO ENGLISH
I went shopping at a department store last week.
That didn't even make that much sense in English.