In St Petersburg you can find bars and restaurants on Rubinstein Street. Tsvetochki (Цветочки) is a nice and cozy cocktail bar.[0] If you like coffee and books, swing by Podpisnyye Izdaniya (Подписные издания) and buy both.[1]

Wish I could say more but I had very limited time in both cities.

[0] https://goo.gl/maps/GXG46qDKYG62

[1] https://goo.gl/maps/HWmNTADox8o