に滞在していた

was staying in

→ に
phrase Rare #33,735
was staying in Used to describe having stayed or been staying in a place in the past. The に marks the location, and ていた indicates an ongoing past state or action.
JA: 去年、私は京都に滞在していた。
EN: I was staying in Kyoto last year.

彼女は少しに滞在していた

She had been staying there until a little while ago.

彼はかなり長い時間そこに滞在していた

He stayed there for quite a long time.

彼は一時ロンドンに滞在していた

He stayed in London for a while.

私は日本帰ってくる前にずっとボストンに滞在していた

I had been staying in Boston before returning to Japan.