Hello! It sounds like you're planning an exciting trip to Gdansk, Riga, and Tallinn. Here are some travel tips to assist you.

Best Time to Visit:
The best time to visit Gdansk, Riga, and Tallinn is during the warmer months from May to September. These cities have a cool temperate climate so the summers are warm and pleasant while winters can be extremely cold.

Route and Accessibility:
The best way to travel between these cities would probably be by air. Many low-cost airlines operate these routes and there is also the option of the Lux Express, a comfortable coach service connecting these cities. You might also consider hopping on a ferry from Gdansk to Riga or Tallinn.

Accommodation and Booking:
There is a variety of accommodations available in these cities from luxury hotels to budget hostels. It is recommended to book your accommodations in advance via popular booking platforms to ensure availability especially during peak season.

Clothing and Essentials:
Prepare for different weather conditions and pack a sturdy umbrella or raincoat for unexpected showers. Comfortable walking shoes are a must as these cities are known for their beautiful and walkable Old Towns. Don’t forget to also pack a good-quality sunscreen for the summer months.

Health and Safety:
No specific vaccinations are required for these cities, but it's always recommended to be up-to-date on routine vaccines. In general, these are safe cities, but standard travel precautions apply. For instance, take care of your belongings, especially in crowded places.

Local Etiquette and Respect:
The people in these cities are very polite and respectful, and they appreciate it when visitors reciprocate that respect. When visiting places of worship, dressing modestly is considered respectful.