Kronshtadt is an old city-port and fortress located on the island of Kotlin in the Finnish Gulf, close to St Petersburg.

from "Staraya Derevnya" metro station - bus 101
from "Chyornaya Rechka" metro station - mini-bus 405

Also, you can travel to Kronshtadt on a speedboat "Meteor" using a special offer from St Petersburg Card. Departure from "Kunstkamera" pier at Universitetskaya embankment.