mutual visitation; reciprocal visits
Used for formal or organized exchanges of visits between groups, institutions, or countries.
The leaders of both countries continue to make reciprocal visits.
Mutual visits between the sister cities were held again this year.
交流 is broader, covering any kind of exchange or interaction, while 相互訪問 specifically refers to reciprocal visits.
Compound of 相互 (mutual) and 訪問 (visit).