There are so many things to enjoy in Saint Petersburg in every season of the year! As for winter, you can enjoy the sightseeing as usual. The queues are much shorter than in summer. There are various museums, palaces and cathedrals to view. For instance, the State Hermitage Museum (has special facilities for people with limited abilities), St Isaac’s Cathedral, Peter and Paul Fortress and many more.
Popular winter activity is ice-skating. Luckily there are many skating rinks in the city centre that offer skates for rent. You can drink warm tea/coffee there, have some pastries, enjoy the atmosphere and relax in warm tents in case you get cold, so no need to skate at all, just get there for a change of inside stay.
Reindeer sledging, downhill skating and spa vacation (the accessibility issues are discussed individually) are among winter activities. There are necessary facilities in the suburbs of Saint Petersburg. It is easy to get there by car or a specially rented van.