Visiting Dojo's protocol
Since I started my Aikido's journey, I always traveled to seminars or dojos to improve my skills.
The first and foremost thing to do is to ask your sensei if you can visit other dojos during your travels. If you sensei agrees, he will write a recommendation's letter to give to the visiting dojo. This letter will contain your rank and a description of your ability to safely train. It is essential to be skilled in ukemi (rolls and falls) before embarking in the journey.
The second thing is to contact the visiting dojo via email and ask for their permission. A teacher might be offended if you don't follow protocols. When a student is traveling, he is a representative of his dojo, so if he does something unruly it might affect the organization as a whole and his sensei.
Recently, I traveled to France so I contacted Mr. Tissier to ask him for his permission to train at his dojo, the Cercle Tissier. The fact that I have already trained at his seminars and he knows me, so it was easy. Some dojos might ask for proof of insurance before stepping on the mat. France is very strict about that. I have also experienced that in Japan when I attended a seminar, the organizers wanted to make sure that all participants had some form of health insurance.
After training in France, I traveled to the city of Salamanca, Spain to attend a seminar for a few days.
If you are traveling with a group, the travel organizer should contact the organizers of the seminar and he should provide the list of all participants.
If the student is traveling alone, he needs to contact the organizers himself. Sometimes, there are online forms to pay your dues before attending a seminar so then you don't have to bother the organizers but it might be polite to contact them and ask them if you can participate first.
Martial artists must follow traditions and protocols to show their level of training. All trainings happen at the dojo, a technical level is essential but a high level of etiquette shows your true level as a martial artist.