Ferries listed are primarily across the Baltic to Sweden, Finland, Germany and other Baltic states. There are now some services included from Eastern Russia.
The Baltic ports provide access to Western Russia with St Petersburg and Moscow reachable by car or train.
Russia is of course vast and one option would be to focus on one part of it. Dipping into locations across its expanse would likely prove expensive requiring flights or long train journeys.
European Russia offers many cultural and architectural highlights. St Petersburg and Moscow offer contrasting city experiences. Saint Petersburg the Imperial capital of Russia founded by Peter the Great has a historic centre with many Baroque and neoclassical buildings preserved from the 18th and 19th centuries. There are many museums, libraries, theatres and galleries to visit, with a number of carnivals through the year and ballet has a special place in the culture of the city.