Know Before You Go
The Northern Forts are all near Kronstadt. Go to the subway station "Chernaja Rechka" (Black River) and take a minibus to Kronsdadt and go forward. The way to Kronsdatd is through the dike. Please note that the minibuses don't stop on the dam because of police restrictions.
The best season to visit the fort is in winter when the ice is frozen. This will allow you to walk in any direction by foot on the lake.
Otherwise, a motor boats should be hired in Kronstadt for transport.