Posted September 13th, 2017, 08:38 PM
I agree with the excellent advice you've already been given.
Those independently-booked shared tours in St Petersburg have exactly the same visa-free status as ships' tours, though cruise lines' phraseology can mislead you into thinking otherwise.
You do need a pre-booked tour, whether thro the ship or thro one of those very good local operators, because to go thro immigration without a tour ticket you must have a visa, which is expensive & complicated. But if you book with a local operator you don't pay with booking & most don't even want a credit card number - they trust you. You print-off the e-mailed tour tickets that they send you, you pay during your tour by cash or card.
Be on deck or your balcony for the glorious sail-in to Stockholm through the archipelago of islands, most so close that you feel that you can reach out and touch the trees. If mother can handle the hop-on ferries, that's the way to see Stockholm. Use the stop at Gamla Stan then mebbe walk thro the old town & past the Royal Palace to the next ho-ho stop. And stop at the historic ship Vasa, housed in a museum.
Helsinki there's probably a ship's shuttle to the Market Place, then either a circular tram ride or a boat trip out to Suomenlinna.
Tallinn there'll be a ship's shuttle to old town, but it goes to the lower part. Things to see & do in the lower part, but Len's suggestion of a taxi to the top of old town & then walk down is a good one.
Anyone who looks like their passport photo is too ill to travel (Will Kommen)