Are the streets made of cobblestones? Hilly?
All the ship excursions are walking.
There is one hill, called Toompea, but there is a gentle way up it (Pikk Street). The rest of the Old Town is flat. There are cobblestones in places and the sidewalks are a bit uneven, but these are not obstacles unless you have a major mobility issue. They are designed for walking on, after all.
The streets are almost all cobblestone and very uneven. That said there is very little car traffic. Also, the hills are minimal except for the one big hill to the upper town.