Banshiki Restaurant
Banshiki is a super nice Russian cuisine restaurant located just off Nevsky Prospekt near Moskovsky railway station (where the trains from Moscow arrive to). The restaurant is adjacent to Degtyarnye Saunas, which offers a really good Russian sauna (banya) experience, so you can plan to visit it after the ritual.
The food is the Russian cuisine, made with love and super delicious. You can have hearty breakfasts that include the real Russian kasha (porridge) and draniki (potatoe pancakes) with sour cream — for €10 both, which is not much. They also have a great selection of herbal teas (try their Taezhny Sbor). The main courses are also really good-looking: meats, fishes, potatoes, vareniki (vegetable ravioli) and other great stuff from the Russian cuisine.
The interior is very stylish: wood and brick walls, very chill and stylish at the same time. A great place both to spend a few hours on a laptop or to have a romantic dinner.
On weekends it's better to book the table before coming. They're open daily from 11.00 am to 1.00 am. As the train station is only within a 5-minute walk it's a great place to have a breakfast / lunch when you arrive or to have a hearty dinner before you depart to Moscow.