へ泳ぎに行った

went swimming at

→ へ
phrase Rare #26,603
went swimming at A past-tense phrase meaning that someone went somewhere in order to swim. The place before へ is the destination, and 泳ぎに行った means “went to swim.”
JA: 先週末、友達と海へ泳ぎに行った。
EN: We went swimming at the beach last weekend.

私はヒロコへ泳ぎに行った

I went swimming at the lake with Hiroko.

学校が終わってから私たちはプールへ泳ぎに行った

After school, we went to the pool to swim.

私たちはへ泳ぎに行った

We went to the beach to swim.

私たちはへ泳ぎに行った

We went swimming in the lake.