St. Petersburg is a sea port and there are a lot of places to feel the soul of the sea and enjoy the sun and the beach, even if it is not a summer now. My favourite place is Beach Laskovyi close to Solnechnoye. It is easy to get there even with public transport: every half an hour there is a train from Finland Railway Station (check the Finnish Railway station article) and at almost the same frequency a small bus (marshrutka) from Chernaya rechka, Prospekt Prosveshenia or Staraya Derevnya underground station.
The beach is sandy and full of pines and firs and some stones and I enjoy going for a really long walk along the Finnish Gulf. There are some restaurants and cafes perfect for a break and to enjoy some lunch close to the sea shore.
Enjoy the solitude and peace during the winter season and the happy crowds swimming, sun bathing and playing beach volleyball during the sunny weekends of the summer.