Traveling (safr) to the land of the unbelievers is impermissible unless three conditions are met: (a) That the person has knowledge to repel doubts. (b) That he has religious belief which will prevent him from falling into lustful desires. (c) There is a need to travel. If these conditions are not met he is not allowed to travel to the land of the unbelievers.
As for some (genuine) need like medical treatment or acquiring knowledge that is not found in his land, and he has knowledge and religious belief as we have described above, then there is no harm in it. As for traveling for tourism to the land of the unbelievers, then there is no need for that, also, it is possible for him to go to the lands of the Muslims to safeguard the manifest symbols of Islam for his family. Our lands, and all praise is due to Allah, have become tourist attractions where one may possibly go.
/ *Please note that there are opposite positions from Taha al Alwani, Yusuf al Qaradawi or Tariq Ramdan, available on this site.*